Select the statement(s) that are true about the enthalpy of a system.

Question

A) Heat is released by every reaction.
B) Enthalpy is a measure of thermal energy under certain conditions.
C) Enthalpy of an isolated system is constant.
D) Enthalpy is measured in temperature degrees.
E) For an endothermic reaction to take place, heat must be absorbed by the surroundings.

Answer 1

Let's evaluate each statement about the enthalpy of a system:

A) Heat is released by every reaction.
This statement is false. While some reactions are exothermic (release heat), others are endothermic (absorb heat).

B) Enthalpy is a measure of thermal energy under certain conditions.
This statement is true. Enthalpy is indeed a measure of thermal energy, specifically under constant pressure.

C) Enthalpy of an isolated system is constant.
This statement is true. In an isolated system, no energy is exchanged with the surroundings, so the total enthalpy remains constant.

D) Enthalpy is measured in temperature degrees.
This statement is false. Enthalpy is measured in joules (or calories), not in temperature degrees.

E) For an endothermic reaction to take place, heat must be absorbed by the surroundings.
This statement is false. An endothermic reaction absorbs heat from the surroundings, not the other way around.

Based on the evaluation:

• True statements: B and C.

Answer 2

Select the statement that is not a factor that affect the heat of reaction.

A) Physical state of reactants or products are factors that affects the heat of reaction.
B) Constant pressure is a factor that affects the heat of reaction.
C) Change in work is a factor that affects the heat of reaction.
D) Different intermediate reactions are factors that affects the heat of reaction.

Answer 3

To determine which statement is not a factor that affects the heat of reaction, let's evaluate each option:

A) Physical state of reactants or products are factors that affects the heat of reaction.
This statement is true. The physical state (solid, liquid, gas) can influence the enthalpy changes during a reaction.

B) Constant pressure is a factor that affects the heat of reaction.
This statement is true. The heat of reaction (enthalpy change) is often defined under constant pressure, and this condition can influence the measured heat changes.

C) Change in work is a factor that affects the heat of reaction.
This statement is false. While work done in a system (like compression) can affect the total energy balance, it doesn’t directly affect the heat of reaction itself as it is typically measured. The heat of reaction is focused on the energy changes due to reactants transforming into products rather than work.

D) Different intermediate reactions are factors that affects the heat of reaction.
This statement is true. The pathways and intermediates can influence the overall energy change of a reaction because they can alter the enthalpy values.

In summary, the statement that is not a factor affecting the heat of reaction is:

C) Change in work is a factor that affects the heat of reaction.

Answer 4

Select the statement(s) that accurately describe a calorimeter.

A) In a calorimeter, if ΔT is negative, then the reaction is endothermic.
B) In a calorimeter, if ΔT is positive, then the reaction is endothermic
C) In a calorimeter the total internal energy remains constant.
D) In a calorimeter, if specific heat capacity is low, then more heat energy is required.
E) In a calorimeter, if specific heat capacity is high, then more heat energy is required

Answer 5

Let's evaluate each statement regarding a calorimeter:

A) In a calorimeter, if ΔT is negative, then the reaction is endothermic.
This statement is true. A negative change in temperature (ΔT) means that the system absorbed heat from the surroundings; therefore, the reaction is endothermic.

B) In a calorimeter, if ΔT is positive, then the reaction is endothermic.
This statement is false. A positive change in temperature means that the system released heat to the surroundings, indicating an exothermic reaction.

C) In a calorimeter the total internal energy remains constant.
This statement is false. The total internal energy can change as heat is absorbed or released during a reaction, even though the calorimeter may isolate the system from the environment.

D) In a calorimeter, if specific heat capacity is low, then more heat energy is required.
This statement is false. If the specific heat capacity is low, less heat energy is required to change the temperature of the substance.

E) In a calorimeter, if specific heat capacity is high, then more heat energy is required.
This statement is true. A high specific heat capacity means that more heat energy is required to achieve a given temperature change.

In summary, the statements that accurately describe a calorimeter are:

• A) In a calorimeter, if ΔT is negative, then the reaction is endothermic.
• E) In a calorimeter, if specific heat capacity is high, then more heat energy is required.