Pre-Lab Experiment 3 Quiz

Chapter 1. Pre-lab Experiment 6: Calorimetry

Introduction

Pre-Lab Experiment 3 Quiz

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1.1 Question 1

Consider the following hypothetical reactions

A + 2B → AB₂ DH = - XX kJ

2A + 5B → A₂B₅ DH = - XX kJ

What is the enthalpy change for the reaction?
2 AB₂ + B → A₂B₅

Consider the following hypothetical reactions

A + 3B → AB₃ DH = - XX kJ

A + 4B → AB₄ DH = - XX kJ

What is the enthalpy change for the reaction?
AB₃ + B → AB₄

Consider the following hypothetical reactions

A + B₂ → AB₂ DH = + XX kJ

4A + 5B₂ → 2A₂B₅ DH = - XX kJ

What is the enthalpy change for the reaction?
4AB₂ + B₂ → A₂B₅

Question 2

Two solid objects, A and B, are both at room temperature and then placed in boiling water and allowed to come to temperature there. Each is then lifted out and placed in separate beakers containing 1000 g of water at 10.0 ^oC. Object A increases the water temperature by 1.50 ^oC; B also increases the water temperature by 1.50 ^oC. In neither case does a chemical reaction occur.

Which statement must be true?

The mass of objects A and B are equal.

The heat capacity of objects A and B are equal.

The specific heats of objects A and B are equal.

Statements (a), (b) and (c) are all true.

Statements (a), (b), and (c) are all false.

Correct.

Incorrect.

Two solid objects, A and B, are both at room temperature and then placed in boiling water and allowed to come to temperature there. Each is then lifted out and placed in separate beakers containing 1000 g of water at 10.0 ^oC. Object A increases the water temperature by 7.20 ^oC; B also increases the water temperature by 1.50 ^oC. In neither case does a chemical reaction occur.

Which statement must be true?

The mass of objects A and B are equal.

The heat capacity of objects A and B are equal.

The specific heats of objects A and B are equal.

Statements (a), (b) and (c) are all true.

Statements (a), (b), and (c) are all false.

Correct.

Incorrect.

Two solid objects, A and B, are both at room temperature and then placed in boiling water and allowed to come to temperature there. Each is then lifted out and placed in separate beakers containing 1000 g of water at 10.0 ^oC. Object A increases the water temperature by 1.20 ^oC; B also increases the water temperature by 6.50 ^oC. In neither case does a chemical reaction occur.

Which statement must be true?

The mass of objects A and B are equal.

The heat capacity of objects A and B are equal.

The specific heats of objects A and B are equal.

Statements (a), (b) and (c) are all true.

Statements (a), (b), and (c) are all false.

Correct.

Incorrect.

Question 3

The reaction between reactant A (smaller spheres) and reactant B (larger spheres) is shown in the diagram.

When xx g of AX (s) dissolves in xx g of water in a coffee-cup calorimeter the temperature rises from xx oC to xx oC. Calculate the enthalpy change (in kJ/mol) for the solution process
AX (s) --> A+ (aq) + X- (aq)

Assume the specific heat of the solution is the same as that of pure water. AX = xx g/mol

Question 4

Hess’s law states that, if a reaction is carried out in a series of steps, DH for the overall reaction equals the sum of the enthalpy changes for the individual stepts. Which statement correctly describes the calculation of DH using Hess’s law?

Reversing a reaction increases the magnitude of DH for the reaction.

Reversing a reaction changes the sign of DH for the reaction.

Multiplying the coefficients of the equation changes the sign of DH for the reaction.

Multiplying the coefficients of the equation makes an exothermic reaction become endothermic (and an endothermic reaction become exothermic).

Correct.

Incorrect.

Question 5

When determining the DH for a neutralization reaction involving NaOH and HCl in a coffee-cup calorimeter, what assumption is NOT reasonable?

The reaction of NaOH with HCl is stoichiometric and no side reactions occur.

The specific heats of NaOH, HCl , and the product of the reaction are the same as that of water.

There will not be a limiting reactant because a strong acid is reacting with a strong base.

Even though some heat may be gained or lost from the coffee-cup and the environment, it is possible to obtain the final temperature by extrapolation from a graph of time versus temperature.

Correct.

Incorrect.

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