Q: Which of the following is the correct formula for calculating the heat absorbed or released by a solution in a calorimeter?

$$q_{\text{soln}} = C_s m_{\text{soln}} \Delta T$$

Question 1

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

Accepted Answer

Energy can be converted from one form to another, but it is neither created nor destroyed.

Question 2

A chemical reaction occurs in a closed system. If the system absorbs 150 J of heat from the surroundings and does 50 J of work on the surroundings, what is the change in internal energy ($$\Delta E) of $$the system?

Accepted Answer

$$\Delta E = 100\ \mathrm{J}$$

Question 3

Which of the following is NOT a state function?

Accepted Answer

Work ($$w)$$

Question 4

Which equation correctly relates the change in internal energy to heat and work?

Accepted Answer

$$\Delta E = q + w$$

Question 5

A reaction is carried out at constant pressure and the system does 75 J of work on the surroundings while releasing 200 J of heat. What is $$\Delta H$$ for the reaction?

Accepted Answer

$$\Delta H = -200\ \mathrm{J}$$

Question 6

Which of the following statements about enthalpy ($$H) is $$FALSE?

Accepted Answer

Enthalpy is path dependent.

Question 7

Which of the following best describes an exothermic process?

Accepted Answer

$$\Delta H \u003c 0$$; heat is released by the system.

Question 8

A reaction is performed in a bomb calorimeter (constant volume) and releases 500 J of heat. What does this value represent?

Accepted Answer

The change in internal energy ($$\Delta E) of $$the reaction.

Question 9

Which of the following is the correct formula for calculating the heat absorbed or released by a solution in a calorimeter?

Accepted Answer

$$q_{	ext{soln}} = C_s m_{	ext{soln}} \Delta T$$

Question 10

Which of the following is true about the standard enthalpy of formation ($$\Delta H_f^\circ) $$for an element in its standard state?

Accepted Answer

$$\Delta H_f^\circ is $$zero.

Question 11

Given the reaction: $$\mathrm{CH_4$(g) + 2 O_2$(g) \rightarrow CO_2$(g) + 2 H_2O(l)}$$, and the following standard enthalpies of formation: $$\Delta H_f^\circ (\mathrm{CH_4$(g)}) = -75\ \mathrm{kJ/mol}$$, $$\Delta H_f^\circ (\mathrm{CO_2$(g)}) = -394\ \mathrm{kJ/mol}$$, $$\Delta H_f^\circ (\mathrm{H_2O(l)}) = -286\ \mathrm{kJ/mol}$$, what is $$\Delta H_{rxn}$$?

Accepted Answer

$$\Delta H_{rxn} = -890\ \mathrm{kJ}$$

Question 12

Which of the following best describes Hess’s Law?

Accepted Answer

The enthalpy change for a reaction is the sum of the enthalpy changes for each step in the reaction.

Question 13

Which of the following statements about bond enthalpy is correct?

Accepted Answer

Bond enthalpy is always positive because energy is required to break bonds.

Question 14

Which of the following reactions is most likely to be endothermic based on bond enthalpies?

Accepted Answer

A reaction where the total bond enthalpy of bonds broken is greater than that of bonds formed.

Question 15

Which of the following best describes an open system?

Accepted Answer

A system that can exchange both heat and mass with its surroundings.

Question 16

A sample of water (mass = 100 g, specific heat = $$4.18\ \mathrm{J/g\cdot K}) is $$heated from $$25.0\ ^\circ\mathrm{C} to$$ $$75.0\ ^\circ\mathrm{C}. $$How much heat is absorbed by the water?

Accepted Answer

$$q = 20,900\ \mathrm{J}$$

Question 17

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

Accepted Answer

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

Question 18

Which of the following best explains why $$q$$ and $$w$$ are not state functions?

Accepted Answer

They depend on the path taken between the initial and final states.

Question 19

If a reaction in a calorimeter causes the temperature of the water to decrease, which of the following is true?

Accepted Answer

The reaction is endothermic.

Thermochemistry: Energy, Enthalpy, and Calorimetry

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