Q: Which equation is used to calculate the standard enthalpy change of a reaction ($$\Delta H^0$_r) $$from standard enthalpies of formation?

$$\Delta H^0$_r = \sum \nu_j \Delta H^0$_f (products) - \sum \nu_i \Delta H^0$_f (reactants)$$

Question 1

Which of the following best describes a thermodynamic system?

Accepted Answer

All materials involved in the process under study, separated from the surroundings by a boundary.

Question 2

Which property is a state function and why?

Accepted Answer

Internal energy, because its change depends only on the initial and final states, not the path taken.

Question 3

A gas expands against a constant external pressure. Which equation correctly describes the work done by the gas?

Accepted Answer

$$w = -P \Delta V$$

Question 4

Which of the following is a path variable in thermodynamics?

Accepted Answer

Heat ($$q)$$

Question 5

A catalyst lowers the activation energy of a reaction. Which statement is correct regarding the effect of a catalyst?

Accepted Answer

It increases the rate of reaction by providing an alternate pathway with lower activation energy.

Question 6

Which equation represents the First Law of Thermodynamics for a closed system?

Accepted Answer

$$\Delta U_{system} = q + w$$

Question 7

Which of the following statements about enthalpy ($$H) is $$correct?

Accepted Answer

Enthalpy is a state function and its change depends only on the initial and final states.

Question 8

The standard enthalpy of formation ($$\Delta H^0$_f) of $$any element in its most stable form is:

Accepted Answer

$$0 kJ/$$mol

Question 9

Given the reaction: $$C_{12}H$$_{22}$$O_{11}(s) + 12O_2(g) \rightarrow 12CO_2(g) + 11H_2O(l)$$, and the following standard enthalpies of formation: $$\Delta H^0$_f(CO_2$, g) = -393.5 kJ/$$mol, $$\Delta H^0$_f(H_2O, l) = -285.8 kJ/$$mol, $$\Delta H^0$_f(C$$_{12}$$H_{22}O$$_{11}, s) = -2226.1$$ kJ/mol, $$\Delta $$H^0_f$$($$O_2$$, g) = 0$$ kJ/mol. What is the standard enthalpy change ($$\Delta $$H^0_r$) for the reaction?

Accepted Answer

$$-5639.7 kJ/$$mol

Question 10

Which statement about entropy ($$S) is $$correct?

Accepted Answer

Entropy is a state function related to energy dispersal and microscopic disorder.

Question 11

For the reaction $$2NH_3(g) + CO_2$(g) \rightarrow NH_2CONH_2(g) + H_2O(l)$$, given the standard entropies: $$S^0(NH_2$$CONH_2, g) = 174$$ J/mol·K, S^0$(CO_2$, g) = 214 J/$$mol·K, $$S^0(H_2O$$, l) = 70$$ J/mol·K, S^0$(NH_3$, g) = 193 J/$$mol·K, what is the standard entropy change ($$\Delta S^0$_r) $$for the reaction?

Accepted Answer

$$-163 J/$$mol·K

Question 12

Which equation correctly relates the standard Gibbs energy change ($$\Delta G^0$_r) to $$the equilibrium constant ($$K$$)?

Accepted Answer

$$\Delta G^0$_r = -RT \ln K$$

Question 13

A reaction has $$\Delta H^0$_r = 100.59 kJ/$$mol and $$\Delta S^0$_r = 174.98 J/$$mol·K. At what temperature will the reaction $$MgCO_3(s$$) \rightarrow MgO(s) + $$CO_2(g$$)$$ become spontaneous? (Assume $$\Delta $$H^0_r$ and $$\Delta $$S^0_r$ are independent of temperature.)

Accepted Answer

$$574.87 K$$

Question 14

Which statement about spontaneous processes is correct according to the Second Law of Thermodynamics?

Accepted Answer

The total entropy of a system and its surroundings always increases for a spontaneous process.

Question 15

For the reaction $$N_2(g) + 3H_2(g$$) \rightleftharpoons 2NH_3(g)$$ in a 3 L container at equilibrium, the following amounts are found: 0.042$ mol N_2$, 0.516$ mol H_2$, 0.0357$ mol NH_3$. What is the equilibrium constant K_c$?

Accepted Answer

$$4.94$$

Question 16

Which of the following is true for the standard enthalpy of formation ($$\Delta H^0$_f) of $$water?

Accepted Answer

$$\Delta H^0$_f(H_2O, l) = -285.8 kJ/$$mol

Question 17

Which of the following is NOT a correct statement about equilibrium constants in heterogeneous systems?

Accepted Answer

The concentration of pure solids and liquids must be included in the equilibrium expression.

Question 18

Which equation is used to calculate the standard enthalpy change of a reaction ($$\Delta H^0$_r) $$from standard enthalpies of formation?

Accepted Answer

$$\Delta H^0$_r = \sum 
u_j \Delta H^0$_f (products) - \sum 
u_i \Delta H^0$_f (reactants)$$

Basic Thermodynamics in General Chemistry: Laws, State Functions, and Equilibrium

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