Q: Which of the following best describes the difference between $$\\Delta H$$ and $$\\Delta E$$ for a chemical reaction at constant pressure?

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

Q: Which of the following is the correct expression for calculating the enthalpy change of a reaction using standard enthalpies of formation?

$$\\Delta H_{rxn} = \\sum n_p \\Delta H_f^\\circ (products) - \\sum n_r \\Delta H_f^\\circ (reactants)$$

Q: A student finds a gold-colored rock with a mass of 4.7 g. Upon absorption of 57.2 J of heat, its temperature rises from $$25^\\circC to$$ $$57^\\circC. $$What is the specific heat of the rock, and is it consistent with pure gold? ($$c_{Au} = 0.129 J/g$\\cdot$$°C)

$$0.380 J/g$\\cdot$$°C;\ not consistent with pure gold

Q: Which of the following is TRUE about constant-volume calorimetry (bomb calorimetry)?

No PV work is done because $$\\Delta V = 0.$$

Question 1

A 50.0 mL sample of 0.10 M AgNO$$_3 is $$mixed with 50.0 mL of 0.10 M HCl in a coffee-cup calorimeter. The temperature rises from 23.40$$^\circC to 24.21$^\circC. $$The density of the solution is 1.00 g/mL and $$c = 4.184 J/g$\cdot$$°C. What is the enthalpy change ($$\Delta H) $$per mole of AgNO$$_3$$ for the reaction as written?

Accepted Answer

$$-67.8 kJ/$$mol

Question 2

Which of the following statements about pressure-volume (PV) work is CORRECT?

Accepted Answer

If the number of moles of gas increases during a reaction at constant pressure, the system does work on the surroundings.

Question 3

A 3.10 g copper penny at $$-8.0^\circC is $$placed in your pocket and warms to $$37.0^\circC. $$The specific heat of Cu is $$0.385 J/g$\cdot$$°C. How much heat is absorbed by the penny?

Accepted Answer

$$+53.7 J$$

Question 4

A 55.0 g block of Al at $$27.5^\circC $$absorbs $$725 J of $$heat. The specific heat of Al is $$0.900 J/g$\cdot$$°C. What is the final temperature of the Al?

Accepted Answer

$$41.1^\circC$$

Question 5

When 1.073 g of sucrose ($$\mathrm{C$$_{12}$$H_{22}O$$_{11}}$$) is combusted in a bomb calorimeter, the temperature rises from 24.92$$^\circ$$C to 28.33$$^\circ$$C. The calorimeter's heat capacity is 6.011$ kJ/$$^\circ$$C. What is $$\Delta E$ for the combustion of sucrose in kJ/mol?

Accepted Answer

$$-6.54 \times 10^3$ kJ/mol

Question 6

Which of the following best describes the difference between $$\Delta H$$ and $$\Delta E$$ for a chemical reaction at constant pressure?

Accepted Answer

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

Question 7

Calculate the change in internal energy ($$\Delta E) $$when $$2 SO$_2(g$$) $$+ O$_2(g$$) $$\rightarrow$$ $$2 SO$_3(g) at$$ $$1$$ atm and $$25^\circC$$, given $$\Delta H = -1362 kJ/$$mol. ($$R = 8.314 J/$$mol$$\cdotK)$$

Accepted Answer

$$-1359 kJ/$$mol

Question 8

Which of the following is TRUE regarding the standard enthalpy of formation ($$\Delta H_f^\circ$$)?

Accepted Answer

The standard enthalpy of formation of an element in its most stable form is zero.

Question 9

Given the following data, calculate $$\Delta H_{rxn}$$ for $$3 H$_2(g$$) $$+ O$_3(g$$) $$\rightarrow$$ $$3 H$_2O(g$$):

$$2 H$_2(g$$) $$+ O$_2(g$$) $$\rightarrow$$ $$2 H$_2O(g$$) $$\quad \Delta H = -483.6 kJ$$
$$3 O$_2(g$$) $$\rightarrow$$ $$2 O$_3(g$$) $$\quad \Delta H = +285.4 kJ$$

Accepted Answer

$$-868.1 kJ$$

Question 10

A 32.5 g cube of Al at $$45.8^\circC is $$placed in 105.3 g of H$$_2O at$$ $$15.4^\circC. $$The specific heats are $$c_{Al} = 0.903 J/g$\cdot$$°C and $$c_{H_2O} = 4.184 J/g$\cdot$$°C. What is the final temperature at thermal equilibrium?

Accepted Answer

$$17.3^\circC$$

Question 11

Which of the following is the correct expression for calculating the enthalpy change of a reaction using standard enthalpies of formation?

Accepted Answer

$$\Delta H_{rxn} = \sum n_p \Delta H_f^\circ (products) - \sum n_r \Delta H_f^\circ (reactants)$$

Question 12

A 150 mL sample of 2.00 M Pb(NO$$_3$$)$$_2 is $$mixed with 300 mL of 2.00 M NaI. The temperature rises from $$20.00^\circC to$$ $$36.09^\circC. $$Assuming the solution is pure water ($$d = 1.00 g/mL$$, $$c = 4.184 J/g$\cdot$$°C), what is the enthalpy of reaction per mole of Pb(NO$$_3$$)$$_2$$?

Accepted Answer

$$-30.3 kJ/$$mol

Question 13

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

Accepted Answer

The enthalpy change for a reaction is the same whether it occurs in one step or multiple steps.

Question 14

A student finds a gold-colored rock with a mass of 4.7 g. Upon absorption of 57.2 J of heat, its temperature rises from $$25^\circC to$$ $$57^\circC. $$What is the specific heat of the rock, and is it consistent with pure gold? ($$c_{Au} = 0.129 J/g$\cdot$$°C)

Accepted Answer

$$0.380 J/g$\cdot$$°C;\ not consistent with pure gold

Question 15

Which of the following best describes the sign conventions for $$q$$ and $$w in $$thermochemistry?

Accepted Answer

$$q \u003e 0$$ for endothermic, $$w \u003c 0$$ for work done by the system

Question 16

What is the mass of CO$$_2 (in kg) $$released by burning a 15-gallon tank of gasoline (pure octane, C$$_8H$_{18}$$, density $$0.70 g/mL$$)? ($$1$$ gal $$= 3.7854 L$$, $$M_{C_8H_{18}} = 114.23 g/$$mol, $$M_{CO_2$} = 44.01 g/$$mol)

Accepted Answer

$$1.2 \times 10^2$ kg

Question 17

Which of the following is TRUE about constant-volume calorimetry (bomb calorimetry)?

Accepted Answer

No PV work is done because $$\Delta V = 0.$$

Question 18

A reaction is carried out in a bomb calorimeter and the temperature of the calorimeter increases. Which of the following is TRUE?

Accepted Answer

The reaction is exothermic and $$q_{rxn} is $$negative.

chapter 5 lec 2

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