Podcast
Questions and Answers
A chemical reaction occurs in a closed system with a constant external pressure. If the volume of the system decreases, what is the sign of the work done by the system?
A chemical reaction occurs in a closed system with a constant external pressure. If the volume of the system decreases, what is the sign of the work done by the system?
- Negative, indicating work done by the system.
- Positive, indicating work done on the system. (correct)
- Cannot be determined without knowing the exact pressure and volume change.
- Zero, as the volume change does not affect the work.
In a bomb calorimeter, why is the change in internal energy ($\Delta E$) of the system equal to the heat (q) measured at constant volume?
In a bomb calorimeter, why is the change in internal energy ($\Delta E$) of the system equal to the heat (q) measured at constant volume?
- Because no heat is exchanged with the surroundings, making $\Delta E = q$.
- Because the pressure is kept constant, simplifying the calculation.
- Because the calorimeter is perfectly insulated, eliminating any energy loss.
- Because no work is done ($w = 0$) due to the constant volume, thus $\Delta E = q + w = q$. (correct)
A gas expands from 0.200 L to 2.25 L against a constant pressure of 1.50 atm. What is the work done (w) by the gas in Joules (J)?
A gas expands from 0.200 L to 2.25 L against a constant pressure of 1.50 atm. What is the work done (w) by the gas in Joules (J)?
- -303 J (correct)
- -310 J
- 303 J
- 310 J
A coffee cup calorimeter, typically used at constant pressure, measures the heat flow of a reaction. Under what condition is the enthalpy change ($\Delta H$) of a reaction equal to the heat (q) measured in a coffee cup calorimeter?
A coffee cup calorimeter, typically used at constant pressure, measures the heat flow of a reaction. Under what condition is the enthalpy change ($\Delta H$) of a reaction equal to the heat (q) measured in a coffee cup calorimeter?
When a 2.00 g sample of a new organic compound is burned in a bomb calorimeter with a heat capacity of 9.50 kJ/°C, the temperature of the calorimeter increases by 3.75°C. Determine the change in internal energy ($\Delta E$) for the combustion of the compound.
When a 2.00 g sample of a new organic compound is burned in a bomb calorimeter with a heat capacity of 9.50 kJ/°C, the temperature of the calorimeter increases by 3.75°C. Determine the change in internal energy ($\Delta E$) for the combustion of the compound.
Consider the reaction: $2 C_2H_2(g) + 5 O_2(g) \rightarrow 4 CO_2(g) + 2 H_2O(l)$. Given the standard enthalpies of formation ($\Delta H_f^\circ$) for $CO_2(g)$, $H_2O(l)$, and $C_2H_2(g)$, what is the correct setup to calculate the enthalpy change of the reaction ($\Delta H_{rxn}$)?
Consider the reaction: $2 C_2H_2(g) + 5 O_2(g) \rightarrow 4 CO_2(g) + 2 H_2O(l)$. Given the standard enthalpies of formation ($\Delta H_f^\circ$) for $CO_2(g)$, $H_2O(l)$, and $C_2H_2(g)$, what is the correct setup to calculate the enthalpy change of the reaction ($\Delta H_{rxn}$)?
Given the following formation reactions and their respective $\Delta H_f^\circ$ values:
$2 C(s, gr) + H_2(g) \rightarrow C_2H_2(g)$, $\Delta H_f^\circ = +227.4 \text{ kJ/mol}$
$C(s, gr) + O_2(g) \rightarrow CO_2(g)$, $\Delta H_f^\circ = -393.5 \text{ kJ/mol}$
$H_2(g) + \frac{1}{2}O_2(g) \rightarrow H_2O(l)$, $\Delta H_f^\circ = -285.8 \text{ kJ/mol}$
What is the enthalpy change for the reaction $4CO_2(g) + 2H_2O(l) \rightarrow 2C_2H_2(g) + 5O_2(g)$?
Given the following formation reactions and their respective $\Delta H_f^\circ$ values:
$2 C(s, gr) + H_2(g) \rightarrow C_2H_2(g)$, $\Delta H_f^\circ = +227.4 \text{ kJ/mol}$ $C(s, gr) + O_2(g) \rightarrow CO_2(g)$, $\Delta H_f^\circ = -393.5 \text{ kJ/mol}$ $H_2(g) + \frac{1}{2}O_2(g) \rightarrow H_2O(l)$, $\Delta H_f^\circ = -285.8 \text{ kJ/mol}$
What is the enthalpy change for the reaction $4CO_2(g) + 2H_2O(l) \rightarrow 2C_2H_2(g) + 5O_2(g)$?
If a reaction has a negative enthalpy change ($\Delta H < 0$), which of the following statements is most accurate?
If a reaction has a negative enthalpy change ($\Delta H < 0$), which of the following statements is most accurate?
Consider the hypothetical reaction: $A(g) + B(g) \rightarrow 2C(g)$. You are given the following information:
$\Delta H_f^\circ [A(g)] = 100 \text{ kJ/mol}$
$\Delta H_f^\circ [B(g)] = -50 \text{ kJ/mol}$
$\Delta H_f^\circ [C(g)] = 25 \text{ kJ/mol}$
Calculate the enthalpy change ($\Delta H_{rxn}$) for this reaction.
Consider the hypothetical reaction: $A(g) + B(g) \rightarrow 2C(g)$. You are given the following information:
$\Delta H_f^\circ [A(g)] = 100 \text{ kJ/mol}$ $\Delta H_f^\circ [B(g)] = -50 \text{ kJ/mol}$ $\Delta H_f^\circ [C(g)] = 25 \text{ kJ/mol}$
Calculate the enthalpy change ($\Delta H_{rxn}$) for this reaction.
Which of the following is true regarding the standard enthalpy of formation ($\Delta H_f^\circ$) of an element in its standard state?
Which of the following is true regarding the standard enthalpy of formation ($\Delta H_f^\circ$) of an element in its standard state?
In a calorimetry experiment at constant pressure, a reaction is performed in an aqueous solution open to the atmosphere. If the temperature of the solution decreases, what can be inferred about the reaction?
In a calorimetry experiment at constant pressure, a reaction is performed in an aqueous solution open to the atmosphere. If the temperature of the solution decreases, what can be inferred about the reaction?
Given the reaction: $Mg(s) + 2HCl(aq) \rightarrow MgCl_2(aq) + H_2(g)$. If 0.158 g of $Mg$ reacts in 100.0 mL of solution, causing the temperature to change, what additional information is needed to calculate $q_{reaction}$?
Given the reaction: $Mg(s) + 2HCl(aq) \rightarrow MgCl_2(aq) + H_2(g)$. If 0.158 g of $Mg$ reacts in 100.0 mL of solution, causing the temperature to change, what additional information is needed to calculate $q_{reaction}$?
In a calorimetry experiment, the heat released or absorbed by the reaction ($q_{reaction}$) is related to the heat absorbed or released by the solution ($q_{solution}$). Which of the following statements correctly describes this relationship?
In a calorimetry experiment, the heat released or absorbed by the reaction ($q_{reaction}$) is related to the heat absorbed or released by the solution ($q_{solution}$). Which of the following statements correctly describes this relationship?
Consider a calorimetry experiment where $C_3H_8$ is combusted. What is the correct sequence of steps to determine the enthalpy change per mole of $C_3H_8$?
Consider a calorimetry experiment where $C_3H_8$ is combusted. What is the correct sequence of steps to determine the enthalpy change per mole of $C_3H_8$?
When using a calorimeter made of nested foam cups, what is the primary assumption made about the system?
When using a calorimeter made of nested foam cups, what is the primary assumption made about the system?
Given 13.2 kg of $C_3H_8$ and the molar mass of $C_3H_8$ is 44.09 g/mol, which conversion factor should be used to convert the mass of $C_3H_8$ from kilograms to moles?
Given 13.2 kg of $C_3H_8$ and the molar mass of $C_3H_8$ is 44.09 g/mol, which conversion factor should be used to convert the mass of $C_3H_8$ from kilograms to moles?
In the calculation of heat transfer ($q$) during a calorimetry experiment, what does a negative value of $q_{reaction}$ indicate?
In the calculation of heat transfer ($q$) during a calorimetry experiment, what does a negative value of $q_{reaction}$ indicate?
In a calorimetry experiment, if the temperature of the solution increases after a reaction, what can be concluded about the sign of $\Delta H_{reaction}$?
In a calorimetry experiment, if the temperature of the solution increases after a reaction, what can be concluded about the sign of $\Delta H_{reaction}$?
A calorimeter with a heat capacity ($C_{cal}$) of 4.90 kJ/°C is used to measure the energy released by burning 1.010 g of $C_{12}H_{22}O_{11}$. The temperature changes from 24.92°C to 28.33°C. Which expression correctly calculates the energy released per mole of $C_{12}H_{22}O_{11}$?
A calorimeter with a heat capacity ($C_{cal}$) of 4.90 kJ/°C is used to measure the energy released by burning 1.010 g of $C_{12}H_{22}O_{11}$. The temperature changes from 24.92°C to 28.33°C. Which expression correctly calculates the energy released per mole of $C_{12}H_{22}O_{11}$?
Given that $\Delta H = \Delta E + P\Delta V$, under what conditions are $\Delta H$ and $\Delta E$ most similar for a chemical reaction?
Given that $\Delta H = \Delta E + P\Delta V$, under what conditions are $\Delta H$ and $\Delta E$ most similar for a chemical reaction?
For an exothermic reaction, how does the chemical potential energy of the products compare to that of the reactants, and what happens to the temperature of the system?
For an exothermic reaction, how does the chemical potential energy of the products compare to that of the reactants, and what happens to the temperature of the system?
Consider a chemical cold pack containing $NH_4NO_3$ that dissolves in water. What type of process is this, and what happens to the temperature of the surroundings (e.g., your hand)?
Consider a chemical cold pack containing $NH_4NO_3$ that dissolves in water. What type of process is this, and what happens to the temperature of the surroundings (e.g., your hand)?
Given the reaction $C_3H_8(g) + 5O_2(g) \rightarrow 3CO_2(g) + 4H_2O(g)$ with $\Delta H = -2044 \text{ kJ}$, what amount of heat is released when 2.5 moles of $O_2$ are consumed?
Given the reaction $C_3H_8(g) + 5O_2(g) \rightarrow 3CO_2(g) + 4H_2O(g)$ with $\Delta H = -2044 \text{ kJ}$, what amount of heat is released when 2.5 moles of $O_2$ are consumed?
A reaction occurs in a sealed container where the pressure is kept constant. If the system releases heat to the surroundings, what are the signs of $q$ and $\Delta H$ for the system?
A reaction occurs in a sealed container where the pressure is kept constant. If the system releases heat to the surroundings, what are the signs of $q$ and $\Delta H$ for the system?
If the enthalpy change ($\Delta H$) for a reaction is -500 kJ/mol, and the reaction involves the production of a gas, how would you expect the internal energy change ($\Delta E$) to compare, assuming the reaction is carried out at constant pressure?
If the enthalpy change ($\Delta H$) for a reaction is -500 kJ/mol, and the reaction involves the production of a gas, how would you expect the internal energy change ($\Delta E$) to compare, assuming the reaction is carried out at constant pressure?
In an endothermic reaction, where does the energy required to break bonds in the reactants primarily come from?
In an endothermic reaction, where does the energy required to break bonds in the reactants primarily come from?
How does increasing the amount of reactants affect the enthalpy change ($\Delta H$) in a chemical reaction?
How does increasing the amount of reactants affect the enthalpy change ($\Delta H$) in a chemical reaction?
Which of the following statements accurately describes the relationship between enthalpy and internal energy for reactions involving gases at constant pressure?
Which of the following statements accurately describes the relationship between enthalpy and internal energy for reactions involving gases at constant pressure?
In a calorimetry experiment, 0.158 g of magnesium (Mg) reacts in 100.0 mL of solution. The temperature rises from 25.6°C to 32.8°C. Given the solution's density is 1.00 g/mL and its specific heat capacity is 4.18 J/g°C, what is the enthalpy change of the reaction per mole of Mg, expressed in scientific notation?
In a calorimetry experiment, 0.158 g of magnesium (Mg) reacts in 100.0 mL of solution. The temperature rises from 25.6°C to 32.8°C. Given the solution's density is 1.00 g/mL and its specific heat capacity is 4.18 J/g°C, what is the enthalpy change of the reaction per mole of Mg, expressed in scientific notation?
Why is the enthalpy change ($\Delta H_{rxn}$) an extensive property?
Why is the enthalpy change ($\Delta H_{rxn}$) an extensive property?
Consider the reaction: C(s) + O2(g) → CO2(g) with $\Delta H = -393.5$ kJ. What is the enthalpy change for the reaction 2 CO2(g) → 2 C(s) + 2 O2(g)?
Consider the reaction: C(s) + O2(g) → CO2(g) with $\Delta H = -393.5$ kJ. What is the enthalpy change for the reaction 2 CO2(g) → 2 C(s) + 2 O2(g)?
According to Hess's Law, how is the enthalpy change of an overall reaction determined if the reaction can be expressed as a series of steps?
According to Hess's Law, how is the enthalpy change of an overall reaction determined if the reaction can be expressed as a series of steps?
Given the following reactions and their enthalpy changes:
2 NO(g) + O2(g) → 2 NO2(g) $\Delta H = -173$ kJ
2 N2(g) + 5 O2(g) + 2 H2O(l) → 4 HNO3(aq) $\Delta H = -255$ kJ
N2(g) + O2(g) → 2 NO(g) $\Delta H = +181$ kJ
Calculate the $\Delta H$ for the reaction: 3 NO2(g) + H2O(l) → 2 HNO3(aq) + NO(g)
Given the following reactions and their enthalpy changes:
2 NO(g) + O2(g) → 2 NO2(g) $\Delta H = -173$ kJ
2 N2(g) + 5 O2(g) + 2 H2O(l) → 4 HNO3(aq) $\Delta H = -255$ kJ
N2(g) + O2(g) → 2 NO(g) $\Delta H = +181$ kJ
Calculate the $\Delta H$ for the reaction: 3 NO2(g) + H2O(l) → 2 HNO3(aq) + NO(g)
If a chemical reaction releases heat into its surroundings, what is the sign of $\Delta H_{rxn}$ and what term is used to describe the reaction?
If a chemical reaction releases heat into its surroundings, what is the sign of $\Delta H_{rxn}$ and what term is used to describe the reaction?
A scientist measures the enthalpy change for a reaction to be $\Delta H = -150$ kJ/mol. If the scientist doubles the amount of reactants used, what is the new enthalpy change for the reaction?
A scientist measures the enthalpy change for a reaction to be $\Delta H = -150$ kJ/mol. If the scientist doubles the amount of reactants used, what is the new enthalpy change for the reaction?
Consider the following reaction: A + B → C with $\Delta H = -50$ kJ. If the reaction is reversed (C → A + B), what is the new enthalpy change?
Consider the following reaction: A + B → C with $\Delta H = -50$ kJ. If the reaction is reversed (C → A + B), what is the new enthalpy change?
A reaction occurs in two steps:
Step 1: X → Y, $\Delta H_1 = -200$ kJ
Step 2: Y → Z, $\Delta H_2 = +150$ kJ
What is the overall enthalpy change for the reaction X → Z?
A reaction occurs in two steps:
Step 1: X → Y, $\Delta H_1 = -200$ kJ
Step 2: Y → Z, $\Delta H_2 = +150$ kJ
What is the overall enthalpy change for the reaction X → Z?
What is the standard state condition used for thermodynamic calculations?
What is the standard state condition used for thermodynamic calculations?
What is the purpose of calculating $\Delta H_{rxn}^{\degree}$ in the context of fuel combustion?
What is the purpose of calculating $\Delta H_{rxn}^{\degree}$ in the context of fuel combustion?
A chemical reaction has a negative $\Delta H_{rxn}^{\degree}$ value. Which statement accurately describes this reaction?
A chemical reaction has a negative $\Delta H_{rxn}^{\degree}$ value. Which statement accurately describes this reaction?
Why are fossil fuels considered non-renewable resources?
Why are fossil fuels considered non-renewable resources?
Given the balanced chemical equation for octane combustion: $C_8H_{18}(g) + 12.5 O_2(g) \rightarrow 8 CO_2(g) + 9 H_2O(g)$, what does the coefficient 12.5 represent?
Given the balanced chemical equation for octane combustion: $C_8H_{18}(g) + 12.5 O_2(g) \rightarrow 8 CO_2(g) + 9 H_2O(g)$, what does the coefficient 12.5 represent?
Which of the following is a direct environmental consequence of the combustion of fossil fuels?
Which of the following is a direct environmental consequence of the combustion of fossil fuels?
Why is the enthalpy of formation, $\Delta H_f^{\degree}$, of $O_2(g)$ equal to zero?
Why is the enthalpy of formation, $\Delta H_f^{\degree}$, of $O_2(g)$ equal to zero?
Using the concept plan provided, what conversion factor is specifically used to convert from moles of octane to grams of octane?
Using the concept plan provided, what conversion factor is specifically used to convert from moles of octane to grams of octane?
Consider two hydrocarbons: methane ($CH_4$) and octane ($C_8H_{18}$). Which of the following statements correctly compares their heats of combustion?
Consider two hydrocarbons: methane ($CH_4$) and octane ($C_8H_{18}$). Which of the following statements correctly compares their heats of combustion?
A scientist is calculating the overall enthalpy change for a reaction using Hess's Law. What thermodynamic property is essential for this calculation?
A scientist is calculating the overall enthalpy change for a reaction using Hess's Law. What thermodynamic property is essential for this calculation?
If the U.S. average energy usage is over $10^5$ kWh per person per year, and conservation efforts reduce individual usage by 10%, what is the new approximate energy consumption per person per year?
If the U.S. average energy usage is over $10^5$ kWh per person per year, and conservation efforts reduce individual usage by 10%, what is the new approximate energy consumption per person per year?
Flashcards
Ccal
Ccal
The calorimeter constant; measures heat capacity of calorimeter.
Delta E (ΔE)
Delta E (ΔE)
Change in internal energy of a system during a reaction.
Exothermic Reactions
Exothermic Reactions
Reactions that release heat (ΔH negative).
Endothermic Reactions
Endothermic Reactions
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Enthalpy (H)
Enthalpy (H)
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qcal
qcal
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qrxn
qrxn
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ΔH
ΔH
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Molecular View of Exothermic
Molecular View of Exothermic
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Work (w)
Work (w)
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Molecular View of Endothermic
Molecular View of Endothermic
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Volume Change (ΔV)
Volume Change (ΔV)
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Calorimetry
Calorimetry
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Bomb Calorimeter
Bomb Calorimeter
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Heat Exchange (q)
Heat Exchange (q)
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ΔHrxn
ΔHrxn
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Specific Heat Capacity (Cs)
Specific Heat Capacity (Cs)
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qsoln (heat of solution)
qsoln (heat of solution)
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Molar Mass of Mg
Molar Mass of Mg
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Hess's Law
Hess's Law
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Reversing Reaction
Reversing Reaction
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Extensive Property
Extensive Property
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Heat Transfer in Reactions
Heat Transfer in Reactions
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Formation Reaction
Formation Reaction
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ΔHf° for C2H2
ΔHf° for C2H2
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ΔHf° for CO2
ΔHf° for CO2
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ΔHrxn Calculation
ΔHrxn Calculation
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Total Enthalpy Change
Total Enthalpy Change
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qreaction
qreaction
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Constant Pressure
Constant Pressure
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Molar Mass of C3H8
Molar Mass of C3H8
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Enthalpy Change (
ΔH)
Enthalpy Change ( ΔH)
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kJ/mol
kJ/mol
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Thermal Energy Transfer
Thermal Energy Transfer
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Temperature Change (
ΔT)
Temperature Change ( ΔT)
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Combustion of Octane
Combustion of Octane
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Balanced Equation for Octane
Balanced Equation for Octane
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Enthalpy Change (ΔH°rxn)
Enthalpy Change (ΔH°rxn)
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Heat of Formation (ΔHf°)
Heat of Formation (ΔHf°)
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Molar Mass of Octane
Molar Mass of Octane
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kJ in Energy Calculations
kJ in Energy Calculations
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KJ Required for 1.0 x 10^11 kJ
KJ Required for 1.0 x 10^11 kJ
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Fossil Fuels
Fossil Fuels
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Energy Consumption in the U.S.
Energy Consumption in the U.S.
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Depletion of Fossil Fuels
Depletion of Fossil Fuels
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Study Notes
Thermochemistry
- Chemical reactions involve energy changes
- Energy can be transferred as heat or work
- Heat is the exchange of thermal energy between a system and its surroundings
- Work is done when a force acts over a distance
- The law of conservation of energy states that energy cannot be created or destroyed.
Heating Your Home
- Most homes use fossil fuels for heating
- Factors affecting how much a home's temperature increases include: fuel use, house size, heat loss, and efficiency of burning process.
Nature of Energy
- Chemistry involves energy and matter
- Energy is the capacity to do work
- Work is a force acting over a distance (Work=Force x Distance)
- Energy can be transferred by contact (collisions)
Classification of Energy
- Kinetic energy is the energy of motion (thermal energy is a type of kinetic energy)
- Potential energy is stored energy, associated with the composition and position of an object (energy in a compound is potential)
Law of Conservation of Energy
- Energy cannot be created or destroyed
- Energy can be transferred between objects
- Energy can be transformed from one form to another
Some Forms of Energy
- Electrical energy is associated with the flow of electrical charge
- Thermal energy is associated with molecular motion
- Radiant energy is associated with energy transitions in an atom
- Potential energy is stored within the nucleus of an atom
- Chemical energy is stored in the attachment of atoms or due to their position
Units of Energy
- Joule (J) is the unit for energy, equivalent to the work done when a force of 1 newton acts on an object over a distance of 1 metre.
- 1 J=1N.m, = 1 kg m^2 /s^2
- Calorie (cal) is the energy needed to raise one gram of water by 1°C.
- Kilojoule (kJ) and kilocalorie (kcal) are larger units
Energy Use
- Information in the table shows energy requirements to raise the temperature of one gram of water by 1 °C
- Information in the table shows energy requirements to light a 100-watt bulb for one hour
- Information in the table shows amount of energy used to run 1 mile
Energy Flow and Conservation of Energy
- The system is the material or process being studied, and surroundings are everything else in the universe.
- Total energy change in a universe is always zero
- ∆Energy universe = 0 = ∆Energy system + ∆Energy surroundings.
Internal Energy
- Internal energy is the sum of all kinetic and potential energies in a system
- The change in internal energy depends on the initial and final states of the substance, not the path.
- ∆E equals final energy state minus initial energy state.
State Function
- A state function's value depends only on the initial and final states of a system, not the path taken.
Energy Diagrams
- Energy diagrams show the direction of energy flow during a process.
Energy Flow
- When energy flows out of a system, it flows into the surroundings.
- When energy flows into a system, it must come from the surroundings.
- The system's energy change is equal and opposite to the surrounding's energy change.
How Is Energy Exchanged?
- Energy is exchanged between the system and surroundings through heat (q) and work (w)
- q represents heat energy
- w represents work energy
- Change in internal energy (∆E) = q + w
Energy Exchange
- Energy is exchanged between the system and surroundings either by heat or work.
Heat & Work
- On a smooth table, most of the kinetic energy is transferred from the first ball to the second ball. With a small amount lost through friction.
- On a rough table, most of the kinetic energy of the first ball is lost through friction, less than half is transferred to the second ball.
Heat Exchange
- Heat is the flow of thermal energy between a system and its surroundings due to a temperature difference.
- Heat flow occurs from higher to lower temperatures until thermal equilibrium is reached.
Quantity of Heat Energy Absorbed
- Heat absorbed by a system increases its temperature.
- Heat capacity (C) is the proportionality constant that relates the amount of heat absorbed to the temperature change.
- Heat capacity (C) depends on the object's mass and material. (C = q/∆T)
Specific Heat Capacity
- Specific heat capacity is the amount of heat energy required to raise the temperature of 1 gram of a substance by 1°C.
- Molar heat capacity is the amount of heat energy required to raise the temperature of 1 mole of substance by 1°C
Quantifying Heat Energy absorbed
- Heat absorbed/released depends on the mass, specific heat, and temperature change of the object
- q = m × Cs × ∆T where: (q) = heat absorbed (m) = mass of the substance (Cs) = specific heat of the substance (∆T) = temperature change of the substance
Measuring ∆E
- Calorimetry, at constant volume, determines ΔE for a reaction by measuring heat.
- The surroundings, a bomb calorimeter, are used and insulated to measure temperature changes.
- ΔE = q/calorimeter = Ccal x ∆T
Bomb Calorimeter
- A bomb calorimeter uses constant volume to help measure change in internal energy (ΔE) for a reaction.
Enthalpy
- Enthalpy (H) is the sum of the system's internal energy (E) and the product of pressure and volume (PV)
- Enthalpy change (ΔH) for a reaction at constant pressure is the heat evolved or absorbed
- ΔH is a state function, and is usually similar in value to ΔE but the difference are largest for reactions that produce or consume gasses.
Endothermic and Exothermic Reactions
- A reaction is exothermic if it releases heat. The enthalpy change (∆H) for exothermic reactions is negative.
- A reaction is endothermic if it absorbs heat, the enthalpy change for endothermic reactions is positive.
Molecular View of Exothermic Reactions
- In exothermic reactions, chemical potential energy is converted into heat energy.
- In exothermic reactions, the product molecules of the reaction have less chemical energy than the reactant molecules, releasing the difference as heat.
Molecular View of Endothermic Reactions
- In endothermic reactions, thermal energy is absorbed from the surroundings converted into chemical potential energy.
Enthalpy of Reaction
- Enthalpy change is an extensive property.
- The more reactants used, the larger the enthalpy change is.
Relationships Involving ΔHrxn
- When a reaction is multiplied by a factor, the enthalpy change is also multiplied by the same factor.
- The sign of ΔΗ changes when a reaction is reversed.
Relationships Involving ΔHrxn – Hess's Law
- Hess's Law states that the enthalpy change for a reaction is the sum of the enthalpy changes of the steps involved.
Standard Conditions
- Standard Conditions means that all reactants and products are in their standard states
- Standard enthalpy change (ΔH°) means the enthalpy change at standard conditions
- Standard enthalpy of formation (ΔHf°) means the enthalpy change when 1 mole of a compound is formed from its constituent elements
Formation Reactions
- A formation reaction is the reaction of elements in their standard state to form 1 mole of a pure compound
- Elements are in their standard states when they are in their most stable form
Writing Formation Reactions
- A formation reaction involves forming 1 mole of a compound from its constituent elements in their standard states.
Calculating Standard Enthalpy Change for a Reaction
- The standard enthalpy change for any reaction is the sum of the standard enthalpies of formation of the products minus the sum of the standard enthalpies of formation of the reactants. (ΔΗ= Σ n ΔΗf (products) - Σ n ΔΗf (reactants))
Calculating the Enthalpy Change for the Combustion of Methane
- Using Hess's Law to determine the enthalpy change in the combustion of methane.
Sample - Calculate the Enthalpy Change in the Reaction
- Demonstrates calculating the enthalpy change of a reaction using formation enthalpies
Energy Use and the Environment
- Fossil fuels are a significant energy source but are not renewable.
- Combustion of fossil fuels releases greenhouse gases, contributing to air pollution, acid rain, and global warming.
Global Warming
- CO2 is a greenhouse gas, trapping heat in the atmosphere.
- A steady rise in atmospheric CO2 levels is contributing to a global temperature increase.
Renewable Energy
- Renewable energy sources, such as solar and wind power, reduce dependence on fossil fuels and environmental damage.
- New technologies continue to improve the efficiency of capturing sunlight.
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Description
Explore the principles of thermochemistry, including work done by systems. Understand calorimetry, bomb calorimeters, coffee cup calorimeters, enthalpy, internal enery and how to calculate heat flow in reactions. Learn about constant pressure and volume conditions.
