Question 1

A student mixes 100.0 g of water at $$80.0\ ^\circ\mathrm{C}$$ with 100.0 g of water at $$20.0\ ^\circ\mathrm{C} in an $$insulated container. What is the final temperature of the mixture, assuming no heat is lost to the surroundings? (The specific heat capacity of water is $$4.18\ \mathrm{J/g\cdot ^\circ C}.)$$

Accepted Answer

$$50.0\ ^\circ\mathrm{C}$$

Question 2

Which of the following best describes the first law of thermodynamics?

Accepted Answer

Energy cannot be created or destroyed, only transformed from one form to another.

Question 3

A chemical reaction in a bomb calorimeter releases $$500.0\ \mathrm{J} of $$heat. What is the change in internal energy ($$\Delta E) $$for the reaction?

Accepted Answer

$$\Delta E = -500.0\ \mathrm{J}$$

Question 4

Which of the following statements about exothermic and endothermic reactions is correct?

Accepted Answer

Exothermic reactions release heat to the surroundings.

Question 5

A gas expands against a constant external pressure of $$1.00\ \mathrm{atm}$$ from $$2.00\ \mathrm{L} to$$ $$5.00\ \mathrm{L}. $$What is the work done by the gas in joules? ($$1\ \mathrm{L\cdot atm} = 101.3\ \mathrm{J})$$

Accepted Answer

$$+303.9\ \mathrm{J}$$

Question 6

Which equation correctly relates the change in enthalpy ($$\Delta H) to $$the change in internal energy ($$\Delta E) $$for a reaction at constant pressure?

Accepted Answer

$$\Delta H = \Delta E + P\Delta V$$

Question 7

Which of the following best explains why water is effective at moderating temperature changes in the environment?

Accepted Answer

Water has a high specific heat capacity.

Question 8

Given the following standard enthalpies of formation: $$\Delta H_f^\circ(CO$_2(g)) = -393.5$$\ \mathrm{kJ/mol}$$, $$\Delta H_f^\circ$$(H_2$O(l)) = -285.8\ \mathrm{kJ/mol}$$, and $$\Delta H_f^\circ(C$_6H$_{12}O$_6(s)) = -1273.3$$\ \mathrm{kJ/mol}$$, calculate the standard enthalpy change for the reaction:

C_6H$$_{12}$$O_6(s) + 6O_2(g$$) \rightarrow 6CO_2(g) + 6H_2O(l)$

Accepted Answer

$$-2801.5\ \mathrm{kJ}$$

Question 9

Which of the following is the correct formula for calculating the heat ($$q) $$absorbed or released by a substance?

Accepted Answer

$$q = mC\Delta T$$

Question 10

Which of the following statements about lattice energy is correct?

Accepted Answer

Lattice energy becomes more exothermic as the ionic charge increases.

Question 11

A sample of copper (mass = $$10.0\ \mathrm{g}$$, specific heat capacity $$= 0.385\ \mathrm{J/g\cdot ^\circ C}) is $$heated from $$25.0\ ^\circ\mathrm{C} to$$ $$75.0\ ^\circ\mathrm{C}. $$How much heat is absorbed by the copper?

Accepted Answer

$$192.5\ \mathrm{J}$$

Question 12

Which of the following best describes the energy change when bonds are broken and formed during a chemical reaction?

Accepted Answer

Breaking bonds requires energy; forming bonds releases energy.

Question 13

Which of the following is a correct statement about the system and surroundings in thermochemistry?

Accepted Answer

The system is the part of the universe being studied, and the surroundings are everything else.

Question 14

A reaction has $$\Delta H = +150\ \mathrm{kJ}. $$Which of the following is true?

Accepted Answer

The reaction is endothermic and absorbs heat.

Question 15

Which of the following equations correctly expresses the relationship for the change in internal energy ($$\Delta E) of a $$system?

Accepted Answer

$$\Delta E = q + w$$

Question 16

Which of the following best describes the process occurring in a coffee-cup calorimeter?

Accepted Answer

The reaction occurs at constant pressure and measures $$\Delta H.$$

Question 17

Which of the following is the correct formula for calculating the enthalpy change of a reaction using bond energies?

Accepted Answer

$$\Delta H_{\mathrm{rxn}} = \sum D_{\mathrm{bonds\ broken}} - \sum D_{\mathrm{bonds\ formed}}$$

Question 18

Which of the following is a correct statement about standard enthalpy of formation ($$\Delta H_f^\circ$$)?

Accepted Answer

It is the enthalpy change when 1 mole of a compound forms from its elements in their standard states.

Question 19

Which of the following best explains why the lattice energy of CaO is much greater than that of NaCl?

Accepted Answer

CaO has a higher product of ionic charges than NaCl.

Chapter 9: Thermochemistry

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