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Questions and Answers
What type of energy is not associated with the random motion of atoms and molecules?
What type of energy is not associated with the random motion of atoms and molecules?
Which of the following accurately describes an exothermic process?
Which of the following accurately describes an exothermic process?
In a closed system, which of the following exchanges can occur?
In a closed system, which of the following exchanges can occur?
What is the primary energy source for Earth?
What is the primary energy source for Earth?
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What is the definition of thermochemistry?
What is the definition of thermochemistry?
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What is the primary purpose of a constant-volume calorimeter?
What is the primary purpose of a constant-volume calorimeter?
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Why is it assumed that no heat is lost to the surroundings in a constant-volume calorimeter?
Why is it assumed that no heat is lost to the surroundings in a constant-volume calorimeter?
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In a constant-pressure calorimeter, which kind of reactions can be measured?
In a constant-pressure calorimeter, which kind of reactions can be measured?
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What does the equation $q_{sys} = 0$ indicate in a constant-volume calorimeter?
What does the equation $q_{sys} = 0$ indicate in a constant-volume calorimeter?
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What is represented by $q_{water} = ms riangle T$?
What is represented by $q_{water} = ms riangle T$?
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In the context of calorimetry, what does the symbol $ riangle H$ represent?
In the context of calorimetry, what does the symbol $ riangle H$ represent?
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How is the heat of dilution typically measured?
How is the heat of dilution typically measured?
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What common household item can be used to construct a crude constant-pressure calorimeter?
What common household item can be used to construct a crude constant-pressure calorimeter?
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What is the sign of DH for an endothermic reaction?
What is the sign of DH for an endothermic reaction?
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What amount of heat is absorbed when 1 mole of ice melts at 0°C and 1 atm?
What amount of heat is absorbed when 1 mole of ice melts at 0°C and 1 atm?
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What happens to the sign of DH when a reaction is reversed?
What happens to the sign of DH when a reaction is reversed?
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How much heat is released from the combustion of 1 mole of methane?
How much heat is released from the combustion of 1 mole of methane?
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How many kilojoules are released when 266 g of P4 burns in air?
How many kilojoules are released when 266 g of P4 burns in air?
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What is the heat change when the specific heat of a substance is multiplied by 2?
What is the heat change when the specific heat of a substance is multiplied by 2?
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What distinguishes the specific heat from heat capacity?
What distinguishes the specific heat from heat capacity?
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What must be included in thermochemical equations?
What must be included in thermochemical equations?
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If a reaction has a DH of -3013 kJ, what does this indicate?
If a reaction has a DH of -3013 kJ, what does this indicate?
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In the equation H2O (s) + heat -> H2O (l), how is DH expressed?
In the equation H2O (s) + heat -> H2O (l), how is DH expressed?
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What is the standard enthalpy of formation for any element in its most stable form?
What is the standard enthalpy of formation for any element in its most stable form?
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How is the standard enthalpy of reaction, ΔH°rxn, calculated?
How is the standard enthalpy of reaction, ΔH°rxn, calculated?
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What does Hess's Law state about enthalpy changes?
What does Hess's Law state about enthalpy changes?
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What is the significance of the standard enthalpy of formation (ΔH0f)?
What is the significance of the standard enthalpy of formation (ΔH0f)?
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For the reaction C(graphite) + O2(g) → CO2(g), what is the ΔHºrxn value?
For the reaction C(graphite) + O2(g) → CO2(g), what is the ΔHºrxn value?
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Which of the following is a correct expression for calculating ΔH°rxn?
Which of the following is a correct expression for calculating ΔH°rxn?
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What is the standard enthalpy of formation (ΔH0f) for O2(g)?
What is the standard enthalpy of formation (ΔH0f) for O2(g)?
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In the reaction CS2(l) + 3O2(g) → CO2(g) + 2SO2(g), what is the reported ΔHrxn value?
In the reaction CS2(l) + 3O2(g) → CO2(g) + 2SO2(g), what is the reported ΔHrxn value?
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What does the 'C' represent in the formula qcal = CcalDt?
What does the 'C' represent in the formula qcal = CcalDt?
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Which substance has a standard enthalpy of formation value of 1.90 kJ/mol?
Which substance has a standard enthalpy of formation value of 1.90 kJ/mol?
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Study Notes
Thermochemistry: Fundamentals
- Thermochemistry is the study of heat changes in chemical reactions.
- Energy is the capacity to do work or produce heat.
- Radiant energy originates from the sun.
- Thermal energy is associated with the random motion of atoms and molecules.
- Chemical energy is stored within the bonds of chemical substances.
- Nuclear energy is stored within the nucleus of an atom.
- Potential energy is energy available due to an object's position.
- Energy forms are interchangeable. One form's disappearance necessitates an equal magnitude appearance of another form (Law of Conservation of Energy).
Energy Changes in Chemical Reactions
- Nearly all chemical reactions either release or absorb energy, often in the form of heat.
- Thermal energy is related to the movement of atoms and molecules.
- Heat is the transfer of thermal energy between objects at different temperatures.
- Temperature measures thermal energy.
System and Surroundings
- The system is the specific part of the universe being studied.
- The surroundings are the rest of the universe external to the system.
- The universe encompasses both the system and its surroundings.
Types of Systems
- Open systems exchange both mass and energy.
- Closed systems exchange only energy.
- Isolated systems exchange neither mass nor energy.
Exothermic and Endothermic Processes
- Exothermic processes release heat to the surroundings, indicated by a negative enthalpy change (ΔH < 0).
- Endothermic processes absorb heat from the surroundings, indicated by a positive enthalpy change (ΔH > 0).
Thermodynamics
- Thermodynamics is the field of chemistry that studies energy and its conversion in physical and chemical processes. It allows predictions about whether a particular process will occur.
- Thermodynamics analyzes changes in a system using state properties.
State Functions
- State functions are properties dependent solely on the current state of a system, not the path taken to reach that state. Examples include energy, pressure, volume, and temperature.
- Changes in state functions are determined by initial and final states.
The First Law of Thermodynamics
- Energy can be converted but neither created nor destroyed. The total energy of the universe remains constant.
- The change in a system's internal energy (ΔE) equals the heat exchanged with the surroundings plus/minus the work done on/by the system (ΔE = q + w). Sign conventions apply. (q = heat, w=work)
Work Done by the System
- Work done by a gas on its surroundings is defined as w = -PΔV.
- The work done is dependent on pressure and change in volume.
Calorimetry
- Calorimetry measures heat changes in processes using a calorimeter. Substances respond differently to heat.
- Specific heat is the amount of heat to raise the temperature of 1g by 1°C.
- Heat capacity is the amount of heat to increase the temperature of a given mass by 1°C.
- Heat calculations use q = mcΔT, where q is heat, m is mass, c is specific heat, and ΔT is the temperature change.
Constant-Volume Calorimetry (Bomb Calorimeter)
- Measure heat of combustion.
- Compounds are ignited in a pressurized container (bomb) filled with oxygen immerses in water.
- Heat evolved during combustion increases the temperature of the water.
- Calibrated device to measure temperature changes to calculate heat of combustion.
Constant-Pressure Calorimetry (Styrofoam Cups)
- Simpler device for measuring non-combustion reactions.
- Styrofoam cup is the calorimeter.
- Heat loss to the surroundings is less of a factor.
- Useful for measuring heats of neutralization, solution, and dilution.
Enthalpy
- Enthalpy is a state function that relates to a system's heat content at constant pressure.
- Standard enthalpy of formation (ΔH°f) is the heat change for forming 1 mole of a compound from its elements in their stable form.
Standard Enthalpy of Reaction
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Standard enthalpy of reaction is the enthalpy change for a process at constant pressure.
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Hess's Law states that the enthalpy change for a reaction is the same whether carried out in one step or multiple steps.
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Enthalpy changes can be calculated using standard enthalpies of formation and the balanced equation of the reaction from the principle, ΔH°rxn = ΣnΔH°f(products) - ΣmΔH°f(reactants).
Other topics mentioned
- Calculating heat of combustion
- Heat of solution
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Description
Test your knowledge on the fundamentals of thermochemistry, including the various forms of energy and their transformations during chemical reactions. This quiz covers energy changes, the concept of systems and surroundings, and the Law of Conservation of Energy.
