Question 1

If the chemical equation for a reaction is doubled, what happens to the enthalpy change ($$\Delta H) $$for the reaction?

Accepted Answer

The enthalpy change is doubled.

Question 2

Which of the following statements best describes a state function?

Accepted Answer

It depends only on the initial and final states, not on the path taken.

Question 3

A 250-g sample of water at $$20.0^\circ \mathrm{C} is $$placed in a freezer at $$-20.0^\circ \mathrm{C}. $$What is the sign of $$q_{sys}$$ for the water after it is placed in the freezer?

Accepted Answer

$$q_{sys} is $$negative because the water loses heat to the freezer.

Question 4

After several hours in the freezer, what will be the state of the 250-g water sample originally at $$20.0^\circ \mathrm{C}$$?

Accepted Answer

The water will have turned to ice.

Question 5

Which of the following best describes the relationship between $$\Delta H_{melting}$$ and $$\Delta H_{freezing}$$?

Accepted Answer

The sign of $$\Delta H_{melting} is $$reversed compared to $$\Delta H_{freezing}.$$

Question 6

Which equation correctly expresses the first law of thermodynamics for a closed system?

Accepted Answer

$$\Delta U = q + w$$

Question 7

A piece of 35.8 g zinc is heated from $$20.00^\circ \mathrm{C} to$$ $$28.00^\circ \mathrm{C}. $$The specific heat of zinc is $$0.388 \ \mathrm{J}/(\mathrm{g} \cdot \mathrm{K}). $$How much heat ($$q) is $$required?

Accepted Answer

$$q = 111 \ \mathrm{J}$$

Question 8

Which of the following is true about enthalpy ($$\Delta H) as a $$state function?

Accepted Answer

It depends only on the initial and final states, not the path.

Question 9

In the reaction $$\mathrm{Ca(s) + 2H_2O(l) \rightarrow Ca$$^{2+}$$(aq) + 2OH^-(aq) + H_2$(g)}$$, which method is used to determine the enthalpy change ($$\Delta H) $$when it cannot be measured directly?

Accepted Answer

Hess's Law

Question 10

Given the following reactions and enthalpy changes:
$$\mathrm{H^+(aq) + OH^-(aq) \rightarrow H_2O(l)}; \Delta H = -55.9 \ \mathrm{kJ}$$
$$\mathrm{Ca(s) + 2H^+(aq) \rightarrow Ca$$^{2+}$$(aq) + H_2$(g)}; \Delta H = -543.0 \ \mathrm{kJ}$$
What is the enthalpy change for $$\mathrm{Ca(s) + 2H_2O(l) \rightarrow Ca$$^{2+}$$(aq) + 2OH^-(aq) + H_2$(g)}$$?

Accepted Answer

$$\Delta H = -431.2 \ \mathrm{kJ}$$

Question 11

Which of the following best describes an exothermic reaction?

Accepted Answer

The system releases heat to the surroundings.

Question 12

A chemical system does work on the surroundings and gives off heat. What is the sign of $$q$$ and $$w$$ for the system?

Accepted Answer

$$q \u003c 0$$, $$w \u003c 0$$

Question 13

Which of the following is NOT a state function?

Accepted Answer

Work ($$w)$$

Question 14

Which formula is used to calculate the heat required to change the temperature of a substance?

Accepted Answer

$$q = m \cdot s \cdot \Delta T$$

Question 15

A reaction is run in a beaker and both heat and work drive the chemical reaction. What is the likely temperature change of the reaction mixture compared to room temperature?

Accepted Answer

The mixture will be colder than room temperature.

Question 16

Which of the following is true about the enthalpy change for a process that can be written as the sum of several steps?

Accepted Answer

The enthalpy change for the overall process is the sum of the enthalpy changes for the individual steps.

Question 17

Which of the following is the correct SI unit for energy?

Accepted Answer

joule

Question 18

If a reaction is endothermic, what is the sign of $$\Delta H$$?

Accepted Answer

$$\Delta H is $$positive.

Question 19

Which of the following is a correct statement about significant figures in scientific measurements?

Accepted Answer

Zeros between nonzero digits are significant.

Applications of the First Law of Thermodynamics and Thermochemistry

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