Q: Which equation correctly expresses the relationship for the standard enthalpy of reaction using standard enthalpies of formation?

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

Question 1

Which of the following best describes the First Law of Thermodynamics?

Accepted Answer

Energy cannot be created nor destroyed, but can be transferred between system and surroundings.

Question 2

A 50.0 g block of aluminum at 120.0 ºC is placed in 110.0 g of water at 90.0 ºC in an insulated container. The specific heat capacities are $$0.897 \ \mathrm{J/g \cdot ºC}$$ for Al and $$4.184 \ \mathrm{J/g \cdot ºC}$$ for water. What is the final temperature of the system? (Assume no heat is lost to the surroundings.)

Accepted Answer

Less than 90.0 ºC

Question 3

Which of the following processes is endothermic?

Accepted Answer

Water boiling

Question 4

Calculate the kinetic energy (in kJ) of an electron ($$m = 9.11 	imes 10$$^{-31}$$ \ \mathrm{kg}) $$moving at $$1.59 	imes 10^6$ \ \mathrm{m/s}. $$Use $$KE = \frac{1}{2}mv^2$.

Accepted Answer

$$1.15 	imes 10$$^{-18}$$ kJ

Question 5

A gas expands from 4.3 L to 8.2 L at a constant pressure of 931 mmHg. If the system absorbs 2.3 kJ of energy, what is the change in internal energy ($$\Delta E) of $$the system? ($$1 \ \mathrm{L \cdot atm} = 101.3 \ \mathrm{J}$$, $$1 \ \mathrm{atm} = 760 \ \mathrm{mmHg})$$

Accepted Answer

$$\Delta E = 1.8 kJ$$

Question 6

Which of the following statements about the combustion of propane is true?

Accepted Answer

It is exothermic.

Question 7

If a system loses heat while doing work on the surroundings, what are the signs of $$q$$ and $$w$$?

Accepted Answer

$$q = -$$, $$w = -$$

Question 8

A refrigerator uses 780 kWh of electrical energy per year. How many kilocalories of electricity does it use in three years? ($$1 \ \mathrm{kWh} = 3.60 	imes 10^6$ \ \mathrm{J}$$, $$1 \ \mathrm{kcal} = 4184 \ \mathrm{J})$$

Accepted Answer

201,000 kcal

Question 9

Which of the following represents the formation equation for barium nitrate, $$\mathrm{Ba(NO_3$)_2}$$?

Accepted Answer

$$\mathrm{Ba(s) + N_2$(g) + 3 O_2$(g) \rightarrow Ba(NO_3$)_2(s)}$$

Question 10

Which of the following substances is NOT in its standard state at 25 ºC and 1 atm?

Accepted Answer

$$\mathrm{H(g)}$$

Question 11

Given the reaction: $$4 \mathrm{NH_3$(g)} + 5 \mathrm{O_2$(g)} \rightarrow 4 \mathrm{NO(g)} + 6 \mathrm{H_2O(g)}$$, and the following standard enthalpies of formation: $$\Delta H_f^\circ(\mathrm{NH_3$(g)}) = -45.9 kJ/$$mol, $$\Delta H_f^\circ(\mathrm{NO(g)}) = 90.3 kJ/$$mol, $$\Delta H_f^\circ(\mathrm{H_2O(g)}) = -241.8 kJ/$$mol$$, \Delta H_f^\circ(\mathrm{O_2$(g)}) = 0$$, calculate $$\Delta H_{rxn}^\circ.$$

Accepted Answer

$$-906.6 kJ$$

Question 12

Which of the following best describes thermal equilibrium?

Accepted Answer

When two substances in contact are at the same temperature and no heat flows between them.

Question 13

A sample of copper absorbs 3.53 kJ of heat, which increases its temperature by 25 ºC. What is the mass (in kg) of the copper sample if the specific heat capacity of copper is $$0.385 \ \mathrm{J/g \cdot ºC}$$?

Accepted Answer

0.367 kg

Question 14

Which compound would show the greatest temperature change upon absorbing 25.0 J of heat? (Assume all samples have a mass of 250.0 g)

Accepted Answer

Copper ($$\mathrm{Cu})$$

Question 15

Which equation correctly expresses the relationship for the standard enthalpy of reaction using standard enthalpies of formation?

Accepted Answer

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

Question 16

If the temperature of a water bath goes from 25 K to 50 K, what can be said about the amount of heat absorbed?

Accepted Answer

It will double.

Question 17

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

Accepted Answer

The enthalpy change for an overall reaction is the sum of the enthalpy changes for the individual steps.

Ch.9 - Thermochemistry: Energy, Heat, and Chemical Reactions

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