AP Chemistry: 6.4 Heat Capacity and Calorimetry – Exam Style questions with Answer- MCQ

Question

The graph above shows the changes in temperature recorded for the 2.00 L of H2O surrounding a constant-volume container in which a 1.00 g sample of benzoic acid was combusted. Assume that heat was not absorbed by the container or lost to the surroundings, that the density of H2O is 1.00g/mL, and that the specific heat capacity of H2O is about 4.2J/g⋅°C. Based on this information, estimate how much heat was released from the combustion of the benzoic acid sample.

A 0.013kJ
B 25kJ
C 180kJ
D 210kJ

▶️Answer/Explanation

Ans:B

The heat released from the combustion of benzoic acid was absorbed by the water and can be calculated by q=mcΔT . Estimating from the graph that the temperature change for the water was about 3.0°C and using 2000g as the mass of the water gives q=(2000g)×(4.2J/g⋅°C)×3.0°C=25,200 J, which is approximately equal to 25kJ.

Question

For an experiment, a 20.0 g piece of \(Al\) was placed inside an insulated cup filled with 40.0 g of \(H_2O\). The data are given in the table above. Assuming no heat is absorbed by the container or the surroundings, which of the following equations provides the correct mathematical relationship for the transfer of heat q between \(Al\) and \(H_2O\)?
A \(−q_{Al}=10\times q_{H_2O}\)
B \(−q_{Al}=5\times q_{H_2O}\)
C \(−q_{Al}=2\times q_{H_2O}\)
D \(−q_{Al}=q_{H_2O}\)

▶️Answer/Explanation

Ans:D
Since heat is only transferred between Al and \(H_2O\), based on the law of conservation of energy, the amount of thermal energy (heat) released by Al must equal the amount of heat absorbed by \(H_2O\) , or \(−q_{Al}=q_{H_2O}\).

Question

A student dissolves 8.00 g of \(NH_4NO_3\)(s) in 100. g of \(H_2O(l)\) in a coffee-cup calorimeter. Based on the initial and final temperatures of the mixture in degrees Celsius shown in the diagram above the laboratory setup, what is the calculated ΔTof the water reported to the appropriate number of significant figures?
A −5.500°C
B −5.50°C
C −5.5°C
D −6°C

▶️Answer/Explanation

Ans:C

Based on the scale of the thermometer, the temperature can be read to the nearest marked gradation, or if possible, halfway between. Because the initial temperature reading is 25.5°C
and the final temperature reading is 20.0°C, the reported change in temperature with the correct number of significant figures is 5.5°C.

Question

Refer to the following graph, which shows the heating curve for methane, \(CH_4\)

How much energy is required to melt 64 g of methane at 90 K? (The molar mass of methane is 16 g/mol.)

(A) 0.24 kJ

(B) 3.8 kJ

(C) 33 kJ

(D) 60. kJ

▶️Answer/Explanation

Ans:B

Question

\(NaOH(aq)+HCl(aq) \rightarrow NaCl(aq)+H_{2}O(l)\)

To determine the concentration of a NaOH(aq) solution, a student titrated a 50. mL sample with 0.10 M HCl(aq). The reaction is represented by the equation above. The titration is monitored using a pH meter, and the experimental results are plotted in the graph below.

A student conducted an experiment to determine \(\Delta H^{\circ}_{rxn}\) the reaction between HCl(aq) and NaOH(aq). The student ran two trials using the volumes of HCl(aq) and NaOH(aq) indicated in the table above, and determined the amount of heat released. Which of the following best explains the relationship between X and Y?
(A) Y = 2X, because the volume of HCl(aq) used in trial 2 is twice the volume used in trial 1.

(B) Y = X, because the number of moles of acid and bas reacting with each other is the same in both trials.

(C) \(Y=\frac{2X}{3}\),because the heat is distributed over more particles in trial 2 than in trial 1.

(D) The relationship between X and Y cannot be predicted.

▶️Answer/Explanation

Ans:D

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