$$\Delta H^\circ = \sum \Delta H_f^\circ (\text{products}) - \sum \Delta H_f^\circ (\text{reactants})$$

Question 1

Which of the following is a correct definition of a state function in thermodynamics?

Accepted Answer

A property that depends only on the initial and final states of a system, not on the path taken.

Question 2

Which of the following is NOT a state function?

Accepted Answer

Work ($$w)$$

Question 3

The altitude of a mountain peak is used as an analogy for a state function because:

Accepted Answer

It depends only on the difference in elevation between the base and the peak, not the path taken.

Question 4

According to the first law of thermodynamics, which equation correctly relates the change in internal energy to heat and work?

Accepted Answer

$$\Delta U = q + w$$

Question 5

A gas absorbs 9 J of heat and does 25 J of work by expanding. What is $$\Delta U$$ for the gas?

Accepted Answer

$$-16 J$$

Question 6

Which of the following best describes an exothermic process?

Accepted Answer

Heat is transferred out of the system, $$q is $$negative.

Question 7

Which equation defines enthalpy ($$H$$)?

Accepted Answer

$$H = U + PV$$

Question 8

Under constant pressure, the change in enthalpy ($$\Delta H) is $$equal to:

Accepted Answer

$$q_p$$

Question 9

Which calorimeter measures $$q_p = \Delta H$$?

Accepted Answer

A constant pressure coffee cup calorimeter

Question 10

When the reaction $$CH_4(g) + 2O_2(g$$) \rightarrow $$CO_2(g) + 2H_2O(g$$)$$ is reversed, what happens to $$\Delta H$$?

Accepted Answer

The sign of $$\Delta H$$ reverses and the reaction becomes endothermic.

Question 11

How much energy is released when 128.5 g of methane ($$CH_4) is $$combusted? ($$\Delta H^\circ = -802 kJ$$, molar mass $$CH_4 = 16.0$ g/mol)

Accepted Answer

$$6.44 	imes 10^3$ kJ

Question 12

Which of the following is a correct formation reaction for $$AgCl(s)$$?

Accepted Answer

$$Ag(s) + 1/2Cl_2(g) \rightarrow AgCl(s)$$

Question 13

By definition, what is the standard enthalpy of formation ($$\Delta H_f^\circ) $$for $$O_2(g$$)$$?

Accepted Answer

$$0.0 kJ$$

Question 14

Hess's Law states that:

Accepted Answer

The enthalpy change for a reaction is the same, regardless of the path taken.

Question 15

Which equation is used to calculate the standard enthalpy change for a reaction using enthalpies of formation?

Accepted Answer

$$\Delta H^\circ = \sum \Delta H_f^\circ (	ext{products}) - \sum \Delta H_f^\circ (	ext{reactants})$$

Question 16

If a reaction is multiplied by 1/2, what happens to $$\Delta H$$?

Accepted Answer

$$\Delta H is $$also multiplied by 1/2.

Question 17

Which of the following statements about path dependent functions is correct?

Accepted Answer

They depend on the specific process or path taken between states.

Question 18

Which of the following is true about the enthalpy of formation for elements in their standard states?

Accepted Answer

It is always zero.

Question 19

A bomb calorimeter operates at constant volume. What does it measure?

Accepted Answer

$$q_v = \Delta U$$

Question 20

Which of the following is the correct formation reaction for $$KMnO_4(s$$)$$?

Accepted Answer

$$K(s) + Mn(s) + 2O_2(g) \rightarrow $$KMnO_4$$(s)$$

Thermochemistry: State Functions, Enthalpy, and Hess's Law

Study Guide - Practice Questions