Q: A sample of 50.0 g of water at $$22.0\ ^\circ\mathrm{C}$$ absorbs heat and its temperature rises to $$28.8\ ^\circ\mathrm{C}. If $$the specific heat of water is $$4.184\ \mathrm{J}\ \mathrm{g}^{-1}\ ^\circ\mathrm{C}^{-1}$$, what is the amount of heat absorbed by the water?

$$1.4 \times 10^3$\ \mathrm{J}$$

Q: Which equation correctly relates the heat ($$q) $$absorbed or released by a substance to its mass ($$m$$), specific heat ($$s$$), and change in temperature ($$\Delta T$$)?

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

Q: In a bomb calorimeter experiment, 3.000 kg of water absorbs $$7.89\ \mathrm{kJ} of $$heat and the temperature rises by $$0.629\ ^\circ\mathrm{C}. $$What is the heat capacity ($$C) of $$the calorimeter?

$$1.71 \times 10^3$\ \mathrm{J}/^\circ\mathrm{C}$$

Question 1

Which of the following statements best describes the First Law of Thermodynamics as it applies to chemical reactions?

Accepted Answer

Energy cannot be created nor destroyed in a chemical reaction, but can be converted from one form to another.

Question 2

A sample of 50.0 g of water at $$22.0\ ^\circ\mathrm{C}$$ absorbs heat and its temperature rises to $$28.8\ ^\circ\mathrm{C}. If $$the specific heat of water is $$4.184\ \mathrm{J}\ \mathrm{g}^{-1}\ ^\circ\mathrm{C}^{-1}$$, what is the amount of heat absorbed by the water?

Accepted Answer

$$1.4 	imes 10^3$\ \mathrm{J}$$

Question 3

Which equation correctly relates the heat ($$q) $$absorbed or released by a substance to its mass ($$m$$), specific heat ($$s$$), and change in temperature ($$\Delta T$$)?

Accepted Answer

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

Question 4

In a bomb calorimeter experiment, 3.000 kg of water absorbs $$7.89\ \mathrm{kJ} of $$heat and the temperature rises by $$0.629\ ^\circ\mathrm{C}. $$What is the heat capacity ($$C) of $$the calorimeter?

Accepted Answer

$$1.71 	imes 10^3$\ \mathrm{J}/^\circ\mathrm{C}$$

Question 5

Which of the following reactions is exothermic?

Accepted Answer

$$\mathrm{CH}_4(g) + 2\ \mathrm{O}_2(g) \rightarrow \mathrm{CO}_2(g) + 2\ \mathrm{H}_2\mathrm{O}(g)$$

Question 6

Which of the following best describes an endothermic reaction?

Accepted Answer

The system absorbs energy from the surroundings and $$\Delta E is $$positive.

Question 7

Given the following reactions and their enthalpy changes:

$$\mathrm{C(graphite)} + \mathrm{O}_2(g) \rightarrow \mathrm{CO}_2(g)\ \Delta H^\circ = -393.5\ \mathrm{kJ}$$
$$\mathrm{H}_2(g) + \frac{1}{2}\mathrm{O}_2(g) \rightarrow \mathrm{H}_2\mathrm{O}(l)\ \Delta H^\circ = -285.8\ \mathrm{kJ}$$
$$\mathrm{C}_2\mathrm{H}_6(g) + \frac{7}{2}\mathrm{O}_2(g) \rightarrow 2\mathrm{CO}_2(g) + 3\mathrm{H}_2\mathrm{O}(l)\ \Delta H^\circ = -1559.7\ \mathrm{kJ}$$

What is the standard enthalpy of formation of $$\mathrm{C}_2\mathrm{H}_6(g)$$?

Accepted Answer

$$-84.7\ \mathrm{kJ}\ \mathrm{mol}^{-1}$$

Question 8

Which of the following is the correct expression for the standard enthalpy change of a reaction ($$\Delta H^\circ_{rxn}) $$using standard enthalpies of formation?

Accepted Answer

$$\Delta H^\circ_{rxn} = \sum \Delta H^\circ_{f,\mathrm{products}} - \sum \Delta H^\circ_{f,\mathrm{reactants}}$$

Question 9

A student mixes 100.0 g of lead at $$100.0\ ^\circ\mathrm{C}$$ with 50.0 g of water at $$22.0\ ^\circ\mathrm{C}. $$The final temperature of the mixture is $$28.8\ ^\circ\mathrm{C}. If $$the specific heat of water is $$4.184\ \mathrm{J}\ \mathrm{g}^{-1}\ ^\circ\mathrm{C}^{-1}$$, what is the specific heat capacity of lead?

Accepted Answer

$$0.133\ \mathrm{J}\ \mathrm{g}^{-1}\ ^\circ\mathrm{C}^{-1}$$

Question 10

Which of the following is true about the standard enthalpy of formation ($$\Delta H^\circ_f) of an $$element in its most stable form at $$25\ ^\circ\mathrm{C}$$ and $$1$$ atm?

Accepted Answer

$$\Delta H^\circ_f is $$defined as zero.

Question 11

Which of the following best describes the function of a calorimeter in thermochemistry experiments?

Accepted Answer

It measures the heat exchanged during a chemical reaction.

Question 12

A combustion reaction releases $$9.598\ \mathrm{kJ} of $$heat in a bomb calorimeter. If $$7.89\ \mathrm{kJ} is $$absorbed by the water, what is the heat absorbed by the calorimeter?

Accepted Answer

$$1.71\ \mathrm{kJ}$$

Question 13

Which of the following is a correct application of Hess's Law?

Accepted Answer

The enthalpy change for a reaction carried out in a series of steps is equal to the sum of the enthalpy changes for the individual steps.

Question 14

Which of the following equations represents the standard enthalpy of formation of ethanol ($$\mathrm{C}_2\mathrm{H}_5\mathrm{OH}(l)$$)?

Accepted Answer

$$2\ \mathrm{C(graphite)} + 3\ \mathrm{H}_2(g) + \frac{1}{2}\ \mathrm{O}_2(g) \rightarrow \mathrm{C}_2\mathrm{H}_5\mathrm{OH}(l)$$

Question 15

If the enthalpy of formation of $$\mathrm{CO}_2(g) is$$ $$-393.5\ \mathrm{kJ}\ \mathrm{mol}^{-1}$$ and that of $$\mathrm{H}_2\mathrm{O}(l) is$$ $$-285.8\ \mathrm{kJ}\ \mathrm{mol}^{-1}$$, what is the enthalpy change for the combustion of $$\mathrm{C}_2\mathrm{H}_6(g)$$, given its enthalpy of formation is $$-84.7\ \mathrm{kJ}\ \mathrm{mol}^{-1}$$?

Accepted Answer

$$-1559.7\ \mathrm{kJ}\ \mathrm{mol}^{-1}$$

Question 16

Which of the following is NOT a factor that affects the amount of heat ($$q) $$required to change the temperature of a substance?

Accepted Answer

The color of the substance.

Question 17

Which of the following best explains why the temperature of the surroundings increases during an exothermic reaction?

Accepted Answer

Energy is released from the system to the surroundings as heat.

Thermochemistry: Energy Changes in Chemical Reactions

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