Question 1

Which of the following statements best describes the law of conservation of energy as it applies to chemical reactions?

Accepted Answer

Energy can be transferred between the system and surroundings, but the total energy of the universe remains constant.

Question 2

A 360-g piece of iron (specific heat $$c = 0.449\ \mathrm{J/g\cdot ^\circ C}) is $$dropped into 425 g of water ($$c = 4.184\ \mathrm{J/g\cdot ^\circ C}) at$$ $$24.0^\circ \mathrm{C}. $$The final temperature of both is $$42.7^\circ \mathrm{C}. $$What was the initial temperature of the iron?

Accepted Answer

$$T_{i,\mathrm{iron}} = 248^\circ \mathrm{C}$$

Question 3

Which equation correctly relates the heat capacity $$C of a $$substance to the heat $$q$$ absorbed and the temperature change $$\Delta T$$?

Accepted Answer

$$C = \dfrac{q}{\Delta T}$$

Question 4

A copper penny with mass $$3.10\ \mathrm{g}$$ and specific heat $$c = 0.385\ \mathrm{J/g\cdot ^\circ C} is $$heated from $$-8.0^\circ \mathrm{C} to$$ $$37.0^\circ \mathrm{C}. $$How much heat is absorbed?

Accepted Answer

$$q = 53.7\ \mathrm{J}$$

Question 5

Which of the following best describes an exothermic reaction at the molecular level?

Accepted Answer

The products have less chemical potential energy than the reactants, and the difference is released as heat.

Question 6

Which device is best suited for measuring the energy produced by combustion reactions that yield large amounts of heat and gaseous products?

Accepted Answer

Bomb calorimeter

Question 7

Which of the following is true about specific heat capacity?

Accepted Answer

It is an intensive property and depends only on the identity of the substance.

Question 8

Calculate the work done (in kJ) when a gas expands from $$46\ \mathrm{L} to$$ $$64\ \mathrm{L} at a $$constant external pressure of $$15\ \mathrm{atm}$$. ($$1\ \mathrm{L\cdot atm} = 101.3\ \mathrm{J})$$

Accepted Answer

$$w = -27.3\ \mathrm{kJ}$$

Question 9

Which of the following equations correctly relates the change in internal energy $$\Delta U to $$heat $$q$$ and work $$w$$?

Accepted Answer

$$\Delta U = q + w$$

Question 10

Which statement about enthalpy ($$H) is $$correct?

Accepted Answer

Enthalpy is a state function and only enthalpy changes ($$\Delta H) $$can be measured.

Question 11

Given the reaction: $$2\mathrm{H}_2(g) + \mathrm{O}_2(g) \rightarrow 2\mathrm{H}_2\mathrm{O}(g)$$, $$\Delta H = -483.6\ \mathrm{kJ}$$, what is the enthalpy change for $$3\mathrm{H}_2(g) + \mathrm{O}_2(g) \rightarrow 3\mathrm{H}_2\mathrm{O}(g)$$?

Accepted Answer

$$\Delta H = -725.4\ \mathrm{kJ}$$

Question 12

Which of the following is true regarding the sign of $$\Delta H in $$thermochemical equations?

Accepted Answer

$$\Delta H \u003c 0$$ indicates an exothermic reaction.

Question 13

Which compound below has the highest lattice energy?

Accepted Answer

MgO

Question 14

Which trend is observed in lattice energy as ion size increases?

Accepted Answer

Lattice energy decreases as ion size increases.

Question 15

Which of the following best describes the use of Hess's Law?

Accepted Answer

It allows calculation of the enthalpy change of a reaction by adding the enthalpy changes of a series of steps that lead to the overall reaction.

Question 16

Estimate the enthalpy change for the reaction $$\mathrm{H}_2(g) + \mathrm{Cl}_2(g) \rightarrow 2\mathrm{HCl}(g)$$ using the following bond energies: $$\mathrm{H}-\mathrm{H} = 436\ \mathrm{kJ/mol}$$, $$\mathrm{Cl}-\mathrm{Cl} = 243\ \mathrm{kJ/mol}$$, $$\mathrm{H}-\mathrm{Cl} = 431\ \mathrm{kJ/mol}.$$

Accepted Answer

$$\Delta H = -278\ \mathrm{kJ}$$

Question 17

Which statement about bond energies is correct?

Accepted Answer

Bond breaking is endothermic and bond making is exothermic.

Question 18

Which of the following bonds is the shortest and strongest?

Accepted Answer

C≡C triple bond

Question 19

A student mixes 50.0 mL of 1.00 M HCl and 50.0 mL of 1.00 M NaOH, both at $$22.0^\circ \mathrm{C}$$, in a coffee-cup calorimeter. The temperature rises to $$28.9^\circ \mathrm{C}. $$Assuming the solution has the same density and specific heat as water, what is the heat produced by the reaction?

Accepted Answer

$$q = -2.9 	imes 10^3$\ \mathrm{J}$$

Thermochemistry: Energy, Calorimetry, and Enthalpy in Chemical Reactions

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