IB Chem Sl Energetics / Thermochemistry

1.

When 1 mole of chlorine gas reacts to form hydrogen chloride, the enthalpy change is -184 kJ/mol. Calculate the energy change when 14.2 grams of chlorine reacts completely with hydrogen.

2.

The dissolving of potassium iodide in water is an endothermic process. Which graph shows the temperature changes that occur when potassium iodide is stirred with water until no further change in temperature is observed?

A.

A
B.

B
C.

C
D.

D

Correct Answer
B. B

Explanation
The correct answer is B because it shows a decrease in temperature as the potassium iodide is dissolved in water. This indicates that the process is endothermic, as the system absorbs heat from the surroundings. The other graphs show either no change in temperature or an increase in temperature, which would indicate an exothermic process.

Rate this question:

0

1

3.

Which statement about the given reaction is correct?

A.

The volume increases and the reaction is endothermic.
B.

A solid is produced and the reaction is exothermic.
C.

A solution is produced and the reaction is endothermic.
D.

A solution is produced and the reaction is exothermic.

Correct Answer
B. A solid is produced and the reaction is exothermic.

Explanation
The correct answer is "A solid is produced and the reaction is exothermic." This means that during the reaction, a solid substance is formed and heat is released. The formation of a solid indicates that a chemical reaction has occurred, and the release of heat indicates that the reaction is exothermic.

Rate this question:

4.

Which process is BEST represented by the energy level diagram found below:

A.

Adding ammonium thiocyanate to barium hydroxide
B.

Melting of mercury metal
C.

Sublimation of dry ice
D.

Neutralization of acid and base

Correct Answer
D. Neutralization of acid and base

Explanation
The energy level diagram represents the neutralization of acid and base. In a neutralization reaction, an acid and a base react to form a salt and water. The energy level diagram shows the energy changes that occur during the reaction. Initially, the reactants have higher energy levels, which decrease as the reaction proceeds. The energy level diagram shows a decrease in energy as the reaction progresses, indicating an exothermic reaction, which is characteristic of a neutralization reaction.

Rate this question:

5.

Which of the following statements DOES NOT describe the enthalpy level diagram found below:

A.

The reaction is endothermic.
B.

Energy is absorbed by the system.
C.

The total energy change for bond formation is greater than that for bond breaking.
D.

The product possesses more energy than the reactants.

Correct Answer
C. The total energy change for bond formation is greater than that for bond breaking.

Explanation
The enthalpy level diagram shows that energy is absorbed by the system, indicating an endothermic reaction. It also shows that the product possesses more energy than the reactants. However, the diagram does not indicate that the total energy change for bond formation is greater than that for bond breaking.

Rate this question:

6.

Which of the following statements regarding the reaction below is NOT correct? Heat of reaction is also given.

A.

The energy of the reactants is less than that of the product.
B.

For each mole of the solid product formed in the reaction, 10.2 kJ of heat is released.
C.

The energy involved in bond forming is greater than that of bond breaking.
D.

If the reaction is carried out in an insulated container, the temperature in the container would increase.

Correct Answer
A. The energy of the reactants is less than that of the product.

Explanation
The given statement is incorrect because the energy of the reactants is actually greater than that of the product. In an exothermic reaction, heat is released, indicating that the energy of the reactants is higher than that of the product. This is consistent with the statement that for each mole of the solid product formed, 10.2 kJ of heat is released. The statement that the energy involved in bond forming is greater than that of bond breaking is also correct, as bond formation releases energy while bond breaking requires energy input. If the reaction is carried out in an insulated container, the temperature in the container would increase due to the release of heat.

Rate this question:

7.

The formation of hydrogen iodide from hydrogen and iodine is an endothermic reaction. H-H + I-I→ H-I + H-I What may be deduced from this information?

A.

The total energy change in bond formation is less than that of bond breaking.
B.

The products possess less energy than the reactants.
C.

The formation of H-I bonds absorbs energy.
D.

The number of bonds broken is greater than the number of bonds formed.

Correct Answer
A. The total energy change in bond formation is less than that of bond breaking.

Explanation
The correct answer suggests that the formation of hydrogen iodide from hydrogen and iodine requires the absorption of energy. This is indicated by the fact that the reaction is described as endothermic, meaning that it requires the input of heat or energy to proceed. The statement that the total energy change in bond formation is less than that of bond breaking implies that more energy is needed to break the bonds in the reactants (H-H and I-I) than is released when the new bonds in the product (H-I) are formed.

Rate this question:

8.

When solid potassium chloride is added to water, the temperature of the liquid goes down. Which conclusion can be made from this observation?

A.

The process is exothermic.
B.

The process is endothermic.
C.

Very little potassium chloride dissolves in water.
D.

All solids dissolve with a temperature decrease.

Correct Answer
B. The process is endothermic.

Explanation
When solid potassium chloride is added to water and the temperature of the liquid goes down, it indicates that heat is being absorbed from the surroundings. This suggests that the process is endothermic, as it requires an input of energy to break the bonds between the potassium and chloride ions in the solid and allow them to dissolve in the water.

Rate this question:

9.

When steam is passed through white-hot coke, a reaction occurs and the temperature of the coke falls.What does this indicate?

A.

Coke contains impurities
B.

The reaction is exothermic
C.

Coke is an oxidising agent
D.

The reaction is endothermic

Correct Answer
D. The reaction is endothermic

Explanation
The given answer suggests that the reaction between steam and white-hot coke is endothermic. This means that the reaction absorbs heat from its surroundings, causing the temperature of the coke to decrease.

Rate this question:

10.

A student was asked to write down five pieces of information that could be obtained from the equation below: Which one of the following pieces of information is INCORRECT?

A.

Magnesium chloride is soluble in water
B.

Total energy of the products is greater than that of the reactants
C.

One mole of magnesium produces one mole of hydrogen molecules
D.

Total energy of the products is less than that of the reactants

Correct Answer
B. Total energy of the products is greater than that of the reactants

Explanation
The equation mentioned in the question is likely a chemical reaction equation. According to the law of conservation of energy, the total energy of the products should be equal to the total energy of the reactants. Therefore, the statement "total energy of the products is greater than that of the reactants" is incorrect.

Rate this question:

11.

The equations for three changes are given below: Which of the following changes are endothermic?

A.

Reaction 1 only
B.

Reactions 1 and 3 only
C.

Reactions 1 and 2 only
D.

Reactions 2 and 3 only

Correct Answer
C. Reactions 1 and 2 only