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Questions and Answers
Which of the following statements accurately describes the relationship between enthalpy change (H) and heat (q) at constant pressure?
Which of the following statements accurately describes the relationship between enthalpy change (H) and heat (q) at constant pressure?
- H is always less than q.
- H is always greater than q.
- H is equal to q. (correct)
Enthalpy is solely determined by the internal energy of a system and is independent of pressure and volume.
Enthalpy is solely determined by the internal energy of a system and is independent of pressure and volume.
False (B)
In a chemical reaction, if the enthalpy change (H) is negative, is the reaction endothermic or exothermic?
In a chemical reaction, if the enthalpy change (H) is negative, is the reaction endothermic or exothermic?
exothermic
For an endothermic reaction, the sign of H is always ________.
For an endothermic reaction, the sign of H is always ________.
Given the reaction: A B + 50 kJ, which of the following is true?
Given the reaction: A B + 50 kJ, which of the following is true?
The enthalpy change (H) for a reaction is independent of the physical states of the reactants and products.
The enthalpy change (H) for a reaction is independent of the physical states of the reactants and products.
In an isolated system, which of the following exchanges are possible with the surroundings?
In an isolated system, which of the following exchanges are possible with the surroundings?
State the thermochemical equation for the complete combustion of methane gas ($CH_4$) where 803 kJ of heat is released.
State the thermochemical equation for the complete combustion of methane gas ($CH_4$) where 803 kJ of heat is released.
Match the following terms related to thermochemistry with their correct descriptions.
Match the following terms related to thermochemistry with their correct descriptions.
The total internal energy of a system remains constant during an exothermic process.
The total internal energy of a system remains constant during an exothermic process.
State the mathematical relationship that defines the change in internal energy (ΔE) of a system in terms of heat (q) and work (w).
State the mathematical relationship that defines the change in internal energy (ΔE) of a system in terms of heat (q) and work (w).
A reaction in which heat is absorbed by the system from the surroundings is called an ______ reaction.
A reaction in which heat is absorbed by the system from the surroundings is called an ______ reaction.
Which of the following statements best describes the first law of thermodynamics?
Which of the following statements best describes the first law of thermodynamics?
If the internal energy of the products in a reaction is greater than the internal energy of the reactants, what can be said about the change in internal energy (ΔE) for the reaction?
If the internal energy of the products in a reaction is greater than the internal energy of the reactants, what can be said about the change in internal energy (ΔE) for the reaction?
Match the system type with its exchange properties:
Match the system type with its exchange properties:
Which of the following units is NOT a unit of heat?
Which of the following units is NOT a unit of heat?
Which of the following best describes Hess's Law?
Which of the following best describes Hess's Law?
The standard enthalpy of formation (ΔHf°) for an element in its standard state is always a positive value.
The standard enthalpy of formation (ΔHf°) for an element in its standard state is always a positive value.
What is the standard enthalpy of formation?
What is the standard enthalpy of formation?
According to Hess's Law, if a reaction is reversed, the sign of ΔH is ______.
According to Hess's Law, if a reaction is reversed, the sign of ΔH is ______.
In the equation ΔH = ∑nΔHf°(products) – ∑mΔHf°(reactants), what do 'n' and 'm' represent?
In the equation ΔH = ∑nΔHf°(products) – ∑mΔHf°(reactants), what do 'n' and 'm' represent?
Given the reactions:
$2H_2O_2(l) \rightarrow 2H_2(g) + 2O_2(g) \Delta H = +376 \text{ kJ}$
$2H_2(g) + O_2(g) \rightarrow 2H_2O(l) \Delta H = -572 \text{ kJ}$
What is the enthalpy change for the reaction $2H_2O_2(l) \rightarrow 2H_2O(l) + O_2(g)$?
Given the reactions: $2H_2O_2(l) \rightarrow 2H_2(g) + 2O_2(g) \Delta H = +376 \text{ kJ}$ $2H_2(g) + O_2(g) \rightarrow 2H_2O(l) \Delta H = -572 \text{ kJ}$ What is the enthalpy change for the reaction $2H_2O_2(l) \rightarrow 2H_2O(l) + O_2(g)$?
According to Hess's Law, what is the most important factor determining the overall enthalpy change of a reaction?
According to Hess's Law, what is the most important factor determining the overall enthalpy change of a reaction?
What is the enthalpy change (ΔH) for the reaction $2C(s) + H_2(g) \rightarrow C_2H_2(g)$ given the following information?
$C_2H_2(g) + \frac{5}{2}O_2(g) \rightarrow 2CO_2(g) + H_2O(l) \quad \Delta H= -1299.6 \text{ kJ}$
$C(s) + O_2(g) \rightarrow CO_2(g) \quad \Delta H= -393.5 \text{ kJ}$
$H_2(g) + \frac{1}{2}O_2(g) \rightarrow H_2O(l) \quad \Delta H= -285.8 \text{ kJ}$
What is the enthalpy change (ΔH) for the reaction $2C(s) + H_2(g) \rightarrow C_2H_2(g)$ given the following information? $C_2H_2(g) + \frac{5}{2}O_2(g) \rightarrow 2CO_2(g) + H_2O(l) \quad \Delta H= -1299.6 \text{ kJ}$ $C(s) + O_2(g) \rightarrow CO_2(g) \quad \Delta H= -393.5 \text{ kJ}$ $H_2(g) + \frac{1}{2}O_2(g) \rightarrow H_2O(l) \quad \Delta H= -285.8 \text{ kJ}$
In calorimetry, a ______ is used to measure the heat absorbed or released during a chemical reaction.
In calorimetry, a ______ is used to measure the heat absorbed or released during a chemical reaction.
If a reaction occurs in multiple steps, Hess's Law states that the overall enthalpy change is the average of the enthalpy changes for each individual step.
If a reaction occurs in multiple steps, Hess's Law states that the overall enthalpy change is the average of the enthalpy changes for each individual step.
In the context of Hess's Law, what does $ΔH$ represent?
In the context of Hess's Law, what does $ΔH$ represent?
Hess's Law states that the total enthalpy change for a reaction is the _______ of the enthalpy changes for each step in the reaction.
Hess's Law states that the total enthalpy change for a reaction is the _______ of the enthalpy changes for each step in the reaction.
Given the following reactions:
C(s) + O2(g) → CO2(g) $ΔH$ = –393.5 kJ
CO(g) + ½O2(g) → CO2(g) $ΔH$ = –283.0 kJ
What is the enthalpy change for the reaction C(s) + ½O2(g) → CO(g)?
Given the following reactions: C(s) + O2(g) → CO2(g) $ΔH$ = –393.5 kJ CO(g) + ½O2(g) → CO2(g) $ΔH$ = –283.0 kJ What is the enthalpy change for the reaction C(s) + ½O2(g) → CO(g)?
Consider these thermochemical equations:
2H2(g) + O2(g) → 2H2O(l) $ΔH$ = -572 kJ
H2(g) + O2(g) → H2O2(l) $ΔH$ = -188 kJ
What is $ΔH$ for the decomposition of hydrogen peroxide: 2H2O2(l) → 2H2O(l) + O2(g)?
Consider these thermochemical equations: 2H2(g) + O2(g) → 2H2O(l) $ΔH$ = -572 kJ H2(g) + O2(g) → H2O2(l) $ΔH$ = -188 kJ What is $ΔH$ for the decomposition of hydrogen peroxide: 2H2O2(l) → 2H2O(l) + O2(g)?
Which statement best describes the application of Hess's Law in determining enthalpy changes?
Which statement best describes the application of Hess's Law in determining enthalpy changes?
Match the following terms with their correct descriptions related to Hess's Law:
Match the following terms with their correct descriptions related to Hess's Law:
Flashcards
Thermal Energy
Thermal Energy
Energy associated with the random motion of atoms and molecules.
Heat
Heat
The transfer of thermal energy between objects at different temperatures.
Thermodynamic System
Thermodynamic System
The substance under study in which a change occurs.
Thermodynamic Surroundings
Thermodynamic Surroundings
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First Law of Thermodynamics
First Law of Thermodynamics
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Internal Energy (E)
Internal Energy (E)
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Endothermic process
Endothermic process
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Exothermic process
Exothermic process
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Enthalpy (H)
Enthalpy (H)
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ΔH at Constant Pressure
ΔH at Constant Pressure
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Enthalpy Definition
Enthalpy Definition
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ΔH Sign
ΔH Sign
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Exothermic Reaction
Exothermic Reaction
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Endothermic Reaction
Endothermic Reaction
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ΔH in Exothermic Reactions
ΔH in Exothermic Reactions
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ΔH in Endothermic Reactions
ΔH in Endothermic Reactions
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Hess's Law
Hess's Law
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Standard Enthalpy Change
Standard Enthalpy Change
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ΔH
ΔH
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Equation 1
Equation 1
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Equation 2
Equation 2
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Combustion of C to CO
Combustion of C to CO
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Standard Enthalpy of Formation (ΔHf°)
Standard Enthalpy of Formation (ΔHf°)
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Standard State of an Element
Standard State of an Element
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Calculating ΔH using ΔHf°
Calculating ΔH using ΔHf°
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∑ΔHf°products
∑ΔHf°products
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∑ΔHf°reactants
∑ΔHf°reactants
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ΔHf° of an element in its standard state
ΔHf° of an element in its standard state
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Heat of Combustion
Heat of Combustion
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Study Notes
- Thermochemistry studies the relationship between heat and chemical reactions. '
- Enthalpy explains a reaction and how it changes.
- Hess's Law calculates the change in enthalpy of a reaction.
Lesson 1 - Thermochemistry
- Thermal energy is associated with the random motion of atoms and molecules.
- Heat is the transfer of thermal energy between two bodies at different temperatures.
- The SI unit for heat is the joule.
- Other units of heat include the kilojoule(kJ), calorie(cal), and Calorie(Cal).
- YU 1 cal is equivalent to 4.184 J.
- 1 Cal is equivalent to 1 000 cal.
- A thermodynamic system is the substance under study in which a change occurs.
- Thermodynamic surroundings consist of everything else in the vicinity of the system.
- An open system can exchange mass and heat with its surroundings.
- A closed system can only transfer energy, but not mass.
- An isolated system cannot transfer mass or energy.
- Energy cannot be created or destroyed; it is only exchanged between objects or transformed from one form to another.
- The First Law of Thermodynamics is also known as the Law of Conservation of Energy: when energy is exchanged or transformed, the total amount of energy remains constant.
- Internal energy is the total amount of kinetic and potential energy a system possesses.
- The change in internal energy (ΔE) is calculated as Efinal - Einitial or Eproducts - Ereactants.
- The change in the system's energy equals the negative change in the surroundings' energy, according to the formula: ΔEsystem = -ΔEsurrounding.
- The change in the system's energy is the sum of heat (q) and work (w): ΔEsystem = q + w.
- An endothermic process is a chemical reaction where heat is absorbed by the system, and q is positive.
- An exothermic process is a chemical reaction where heat is released by the system, and q is negative.
Lesson 2 - Enthalpy of a Chemical Reaction
- Enthalpy (H) is the internal energy (E) plus the product of pressure (P) and volume (V): H = E + PV
- ΔH = ΔΕ + PAV
- Enthalpy is the heat content of a chemical system.
- At constant pressure, the change in enthalpy is equal to the heat gained or lost
- ΔH = q.
- Enthalpy is an extensive property.
- The ΔH in the forward and reverse reactions is equal in size but opposite in sign 2H2 + O2 → 2H2O.
- ΔH depends on the state of the products and reactants.
- Thermochemical equations present heat changes
- reactants = products + energy indicates an exothermic reaction.
- reactants + energy = products indicates an endothermic reaction.
- CaO(s) + H2O(1) → Ca(OH)2(s) + 62.5 kJ
- 2NaHCO3(s) + 129 kJ → Na2CO3(s) + H2O(g) + CO2(g)
- ΔΗ = - (exothermic)
- ΔH = + (endothermic) when expressing thermochemical equations with ΔH values.
- Hess Law says if a reaction is carried out in a series of steps, ΔH for the overall reaction will be equal to the sum of the enthalpy changes for the individual steps.
- total enthalpy change depends only on the initial state of the reactants and the final state of the products.
- The enthalpy of reaction for the combustion of C to CO2 is -393.5 kJ/mol C, and the enthalpy for the combustion of CO to CO2 is -283.0 kJ/mol C.
- C(s) + 1/2O2(g) → CO(g)
- ΔΗ=?
- Thermochemical equations are used to determine ΔH for the decomposition of hydrogen peroxide (H2O2).
- standard enthalpy of formation (ΔΗf°) - change in enthalpy that accompanies the formation of one mole of the compound in its standard state
- Elements in their standard states have a ΔΗf° = 0.
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Description
Test your knowledge of enthalpy, heat transfer, and thermochemical equations. This quiz covers exothermic and endothermic reactions, enthalpy changes, and the relationship between enthalpy and internal energy. Review the concepts of thermochemistry.
