Q: Given the reaction: $$2\text{H}_2(g) + \text{O}_2(g) \rightarrow 2\text{H}_2\text{O}(l)$$, $$\Delta H = -571.7\ \text{kJ}. $$What is $$\Delta H$$ for the reverse reaction?

$$\Delta H = +571.7\ \text{kJ}$$

Q: Which of the following is a standard enthalpy of formation reaction?

$$\text{C(graphite)} + 2\text{H}_2(g) \rightarrow \text{CH}_4(g)$$

Q: Using the following standard enthalpies of formation: $$\Delta H_f^\circ(NH$_3(g)) = -46$ kJ/mol, $$\Delta H_f^\circ$$(NO_2$(g)) = 34 kJ/$$mol, $$\Delta H_f^\circ(H$_2O(l)) = -286$ kJ/mol, $$\Delta H_f^\circ$$(O_2$(g)) = 0 kJ/$$mol, calculate $$\Delta H_{rxn}^\circ$$ for: $$4\text{NH}_3(g) + 7\text{O}_2(g) \rightarrow 4\text{NO}_2(g) + 6\text{H}_2\text{O}(l).$$

$$\Delta H_{rxn}^\circ = -1172\ \text{kJ}$$

Question 1

Which statement best describes the First Law of Thermodynamics as articulated by Richard Feynman?

Accepted Answer

Energy is conserved; it can change forms but the total amount remains constant.

Question 2

A chemical reaction occurs in a piston at constant external pressure of 1 atm. The volume of the gas decreases from 4.0 L to 2.0 L. What is the work done by the system ($$w$$)? (1 L·atm = 101 J)

Accepted Answer

$$w = +202\ 	ext{J}$$

Question 3

Which of the following best describes an exothermic process?

Accepted Answer

The system releases heat to the surroundings and $$q is $$negative.

Question 4

A cold pack is applied to an injury. Which statement is correct regarding the sign of $$q$$ for the system (the cold pack)?

Accepted Answer

$$q is $$positive; heat is absorbed by the cold pack.

Question 5

Which equation correctly expresses the relationship between internal energy, heat, and work?

Accepted Answer

$$\Delta E = q + w$$

Question 6

In a coffee-cup calorimeter, 50.0 g of water absorbs heat and its temperature rises by $$2.5^\circC. $$What is the heat absorbed by the water? ($$s = 4.18\ 	ext{J/g}^\circ	ext{C})$$

Accepted Answer

$$q = 523\ 	ext{J}$$

Question 7

Which of the following is a state function?

Accepted Answer

Enthalpy ($$H)$$

Question 8

Given the reaction: $$2	ext{H}_2(g) + 	ext{O}_2(g) ightarrow 2	ext{H}_2	ext{O}(l)$$, $$\Delta H = -571.7\ 	ext{kJ}. $$What is $$\Delta H$$ for the reverse reaction?

Accepted Answer

$$\Delta H = +571.7\ 	ext{kJ}$$

Question 9

Which of the following is a standard enthalpy of formation reaction?

Accepted Answer

$$	ext{C(graphite)} + 2	ext{H}_2(g) ightarrow 	ext{CH}_4(g)$$

Question 10

Using the following standard enthalpies of formation: $$\Delta H_f^\circ(NH$_3(g)) = -46$ kJ/mol, $$\Delta H_f^\circ$$(NO_2$(g)) = 34 kJ/$$mol, $$\Delta H_f^\circ(H$_2O(l)) = -286$ kJ/mol, $$\Delta H_f^\circ$$(O_2$(g)) = 0 kJ/$$mol, calculate $$\Delta H_{rxn}^\circ$$ for: $$4	ext{NH}_3(g) + 7	ext{O}_2(g) ightarrow 4	ext{NO}_2(g) + 6	ext{H}_2	ext{O}(l).$$

Accepted Answer

$$\Delta H_{rxn}^\circ = -1172\ 	ext{kJ}$$

Question 11

Which of the following best explains why some spontaneous reactions are endothermic?

Accepted Answer

Because entropy ($$S) $$increases enough to make $$\Delta G$$ negative.

Question 12

A reaction in a bomb calorimeter causes the temperature of the calorimeter to rise. Which statement is correct?

Accepted Answer

The reaction is exothermic and $$\Delta E is $$negative.

Question 13

Which of the following best describes the energy changes when a hydrogen balloon explodes?

Accepted Answer

Energy is released to the surroundings, $$q is $$negative.

Question 14

Which of the following is true about the relationship between heat and work in a battery discharging to power a fan?

Accepted Answer

The energy lost by the battery is the sum of heat and work done.

Question 15

Which equation correctly expresses Hess's Law?

Accepted Answer

$$\Delta H_3$ = \Delta H_1$ + \Delta H_2$

Question 16

Which energy source contributed the largest share to U.S. energy consumption in 2023?

Accepted Answer

Petroleum

Question 17

If a reaction is carried out at constant volume in a bomb calorimeter, which thermodynamic quantity does the measured heat correspond to?

Accepted Answer

$$\Delta E$$

Question 18

Which of the following is NOT a correct unit conversion?

Accepted Answer

1 J = 100 cal

Question 19

Which of the following best describes the direction of heat flow?

Accepted Answer

Heat always flows from higher temperature to lower temperature.

Thermochemistry and Energy in Chemical Reactions

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