Q: In a calorimetry experiment, $$10.0\ \mathrm{mL} of$$ $$1.00\ \mathrm{M}$$ AgNO$$_3 is $$mixed with $$10.0\ \mathrm{mL} of$$ $$1.00\ \mathrm{M}$$ NaCl$$\ (aq) at$$ $$25.0\ ^\circ\mathrm{C}$$, causing the temperature to rise to $$32.6\ ^\circ\mathrm{C}. $$Assuming the specific heat of the mixture is $$4.18\ \mathrm{J/(g\cdot ^\circ C)}$$ and the density is $$1.00\ \mathrm{g/mL}$$, what is the enthalpy change ($$\Delta H) $$per mole of AgCl formed?

$$-6.41 \times 10^4$\ \mathrm{J/mol}$$

Question 1

A chemical reaction occurs in a cylinder fitted with a movable piston. The reaction causes the gas inside to expand from 12.0 L to 14.5 L against a constant external pressure of 5.0 atm. What is the work done by the system, in kilojoules?

Accepted Answer

$$w = -1.3\ \mathrm{kJ}$$

Question 2

During the synthesis of ammonia, the volume contracts from 8.6 L to 4.3 L at an external pressure of 44 atm. In which direction does the work energy flow, and what is the sign of the work?

Accepted Answer

Work flows to the surroundings; $$w is $$negative.

Question 3

Given the reaction $$\mathrm{N_2$(g) + 3 H_2$(g) \rightarrow 2 NH_3$(g)}$$ with $$\Delta H = -92.2\ \mathrm{kJ}$$, carried out at a constant pressure of $$40.0\ \mathrm{atm}$$ and a volume change of $$-1.12\ \mathrm{L}$$, what is the value of $$\Delta E ($$internal energy change) in kJ? (Use $$1\ \mathrm{L \cdot atm} = 101\ \mathrm{J})$$

Accepted Answer

$$\Delta E = -87.7\ \mathrm{kJ}$$

Question 4

For the reaction $$2\ \mathrm{H_2$(g) + O_2$(g) \rightarrow 2\ H_2O(g)}$$ with $$\Delta H = -484\ \mathrm{kJ}$$, if the volume change is $$-2.44\ \mathrm{L} at$$ $$1.00\ \mathrm{atm}$$, what is the $$P\Delta V$$ work in kJ? (Use $$1\ \mathrm{L \cdot atm} = 101\ \mathrm{J})$$

Accepted Answer

$$w = -0.25\ \mathrm{kJ}$$

Question 5

A reaction has $$\Delta E = -186\ \mathrm{kJ/mol}$$ and occurs at $$1.0\ \mathrm{atm}$$, with the number of moles of gas decreasing from 5 mol to 4 mol. What is the sign of $$P\Delta V$$ and what does this indicate about the magnitude of $$\Delta H$$ compared to $$\Delta E$$?

Accepted Answer

$$P\Delta V is $$positive; $$\Delta H is $$less negative than $$\Delta E.$$

Question 6

How much heat (in kJ) is released when $$5.00\ \mathrm{g} of $$propane ($$\mathrm{C_3H_8}) $$reacts with excess $$\mathrm{O_2$}$$ according to $$\mathrm{C_3H_8(g) + 5 O_2$(g) \rightarrow 3 CO_2$(g) + 4 H_2O(g)}$$, $$\Delta H^\circ = -2044\ \mathrm{kJ}$$?

Accepted Answer

$$231\ \mathrm{kJ}$$

Question 7

Which of the following processes is endothermic?

Accepted Answer

Sweat evaporating from your skin.

Question 8

Which salt, when dissolved in water in a cold pack, would result in the greatest decrease in temperature? Use the following enthalpy changes: $$\mathrm{Li^+(aq) + F^-(aq)}\ \Delta H = +5.5\ \mathrm{kJ}$$, $$\mathrm{Li^+(aq) + Cl^-(aq)}\ \Delta H = -37.1\ \mathrm{kJ}$$, $$\mathrm{Ba$$^{2+}$$(aq) + SO_4$^{2-}(aq)}\ \Delta H = +26.3\ \mathrm{kJ}$$, $$\mathrm{Ca$$^{2+}$$(aq) + 2Cl^-(aq)}\ \Delta H = -81.8\ \mathrm{kJ}.$$

Accepted Answer

CaCl$$_2$$

Question 9

A 5.00 g block of silicon ($$\mathrm{Si}) is $$heated, causing its temperature to rise by $$19.2\ ^\circ\mathrm{C}. If $$the specific heat of silicon is $$0.712\ \mathrm{J/(g\cdot ^\circ C)}$$, how much heat (in J) was absorbed?

Accepted Answer

$$68.3\ \mathrm{J}$$

Question 10

In a calorimetry experiment, $$10.0\ \mathrm{mL} of$$ $$1.00\ \mathrm{M}$$ AgNO$$_3 is $$mixed with $$10.0\ \mathrm{mL} of$$ $$1.00\ \mathrm{M}$$ NaCl$$\ (aq) at$$ $$25.0\ ^\circ\mathrm{C}$$, causing the temperature to rise to $$32.6\ ^\circ\mathrm{C}. $$Assuming the specific heat of the mixture is $$4.18\ \mathrm{J/(g\cdot ^\circ C)}$$ and the density is $$1.00\ \mathrm{g/mL}$$, what is the enthalpy change ($$\Delta H) $$per mole of AgCl formed?

Accepted Answer

$$-6.41 	imes 10^4$\ \mathrm{J/mol}$$

Question 11

Which of the following statements about $$\Delta H$$ and $$\Delta E is $$correct for a reaction in which the number of moles of gas decreases?

Accepted Answer

$$\Delta H is $$less negative than $$\Delta E.$$

Question 12

Which process is exothermic and has a negative $$\Delta H$$?

Accepted Answer

Condensation of water vapor on a bathroom mirror.

Question 13

A reaction occurs at constant pressure and releases $$500\ \mathrm{J} of $$heat while the system does $$200\ \mathrm{J} of $$work on the surroundings. What is the change in internal energy ($$\Delta E) $$for the system?

Accepted Answer

$$\Delta E = -300\ \mathrm{J}$$

Question 14

Which of the following best describes the sign of $$\Delta S$$ for the reaction $$\mathrm{C_6H_{12}O_6$(s) \rightarrow 2 C_2H_5OH(l) + 2 CO_2$(g)}$$?

Accepted Answer

$$\Delta S is $$positive because the number of gas molecules increases.

Question 15

For the reaction $$\mathrm{$$CaCO_3$$(s) \rightarrow CaO(s) + CO_2$(g)}$$ with $$\Delta H = 179\ \mathrm{kJ}$$ and $$\Delta S = 160\ \mathrm{J/K}$$, at what temperature (in K) does the reaction become spontaneous?

Accepted Answer

$$T = 1120\ \mathrm{K}$$

Question 16

Which of the following is true for a process that is endothermic and results in an increase in entropy?

Accepted Answer

The process can be spontaneous at high temperatures.

Thermochemistry: PV Work, Internal Energy, Heat Transfer, and Endo/Exothermic Processes

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