Q: A student mixes 100 mL of 0.5 M AgNO$$_3(aq) $$with 100 mL of 0.5 M KCl(aq) in a calorimeter. The temperature rises by 7.5$$^\circC. If $$the specific heat capacity of the solution is $$4.18\ \mathrm{J\ g$$^{-1}$$\ ^\circ C$$^{-1}$$}$$ and the total mass is 200 g, what is the heat change ($$q) $$for the reaction?

$$q = 4.18 \times 200 \times 7.5 = 6270\ \mathrm{J}$$

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

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

Q: Which of the following is the correct formula for calculating heat change in a calorimeter?

$$q = m \times c \times \Delta T$$

Question 1

Which of the following statements correctly describes an exothermic reaction?

Accepted Answer

The enthalpy of products is less than the enthalpy of reactants, and $$\Delta H is $$negative.

Question 2

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

Accepted Answer

The enthalpy change when 1 mole of a compound is formed from its elements at their standard states (298 K, 1 atm).

Question 3

A student mixes 100 mL of 0.5 M AgNO$$_3(aq) $$with 100 mL of 0.5 M KCl(aq) in a calorimeter. The temperature rises by 7.5$$^\circC. If $$the specific heat capacity of the solution is $$4.18\ \mathrm{J\ g$$^{-1}$$\ ^\circ C$$^{-1}$$}$$ and the total mass is 200 g, what is the heat change ($$q) $$for the reaction?

Accepted Answer

$$q = 4.18 	imes 200 	imes 7.5 = 6270\ \mathrm{J}$$

Question 4

Which of the following enthalpy changes is always positive and why?

Accepted Answer

Enthalpy of atomisation, because it involves only breaking of bonds.

Question 5

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

Accepted Answer

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

Question 6

A 0.45 g piece of copper ($$c = 0.385\ \mathrm{J\ g$$^{-1}$$\ ^\circ C$$^{-1}$$}) at 87.0$^\circC is $$placed in a calorimeter containing water ($$c = 4.184\ \mathrm{J\ g$$^{-1}$$\ ^\circ C$$^{-1}$$}) at 23.0$^\circC. $$The final temperature is 24.8$$^\circC. $$What is the mass of water in the calorimeter?

Accepted Answer

1.4 g

Question 7

Which of the following best describes the difference between a simple calorimeter and a bomb calorimeter?

Accepted Answer

A simple calorimeter assumes no heat loss to surroundings, while a bomb calorimeter does not make this assumption.

Question 8

Which of the following reactions is an example of an endothermic process?

Accepted Answer

Melting of ice cubes

Question 9

Calculate the enthalpy change for the combustion of methane using the following data: $$\Delta H_f^\circ(CH$_4(g)) = -74.8$$\ \mathrm{kJ/mol}$$, $$\Delta H_f^\circ$$(CO_2$(g)) = -394.0\ \mathrm{kJ/mol}$$, $$\Delta H_f^\circ(H$_2O(l)) = -286.0$$\ \mathrm{kJ/mol}$$. The reaction is: CH_4$(g) + 2 O_2$(g) $$\rightarrow$$ CO_2$(g) + 2 H_2$O(l).

Accepted Answer

$$\Delta H = -891.2\ \mathrm{kJ/mol}$$

Question 10

Which of the following is the correct definition of lattice enthalpy (U) in the Born-Haber cycle?

Accepted Answer

The enthalpy change when one mole of solid ionic compound is formed from its ions in the gaseous state.

Question 11

Which of the following is true about the standard enthalpy of formation of an element in its most stable state?

Accepted Answer

It is zero.

Question 12

A piece of titanium metal (20.8 g) is heated to 99.5$$^\circC $$and dropped into 75.0 g water at 21.7$$^\circC. $$The final temperature is 24.3$$^\circC. If $$the specific heat of water is $$4.184\ \mathrm{J\ g$$^{-1}$$\ ^\circ C$$^{-1}$$}$$, what is the specific heat capacity of titanium?

Accepted Answer

$$c = 0.522\ \mathrm{J\ g$$^{-1}$$\ ^\circ C$$^{-1}$$}$$

Question 13

Which of the following is the correct formula for calculating heat change in a calorimeter?

Accepted Answer

$$q = m 	imes c 	imes \Delta T$$

Question 14

Which statement best describes Hess's Law?

Accepted Answer

The enthalpy change of a reaction is independent of the route taken and depends only on the initial and final states.

Question 15

Which of the following is an example of a thermochemical equation for the enthalpy of neutralization?

Accepted Answer

HCl(aq) + NaOH(aq) $$\rightarrow$$ NaCl(aq) + H$$_2O(aq$$); $$\Delta H_n^\circ = -58\ \mathrm{kJ\ $$mol^{-1}$$}$$

Question 16

In the Born-Haber cycle for NaCl, which step corresponds to the electron affinity of chlorine?

Accepted Answer

Cl(g) + e^- $$\rightarrow Cl^-(g)$$

Question 17

Which of the following processes is associated with a negative enthalpy change?

Accepted Answer

Hydration of Na$$^+(g) to Na$^+(aq)$$

Thermochemistry: Chemical Energetics and Calorimetry

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