Ib Chemistry Hl Topic 5

1. State that combustion and neutralization are exothermic processes.

List the steps involved in combustion and neutralization reactions.

Explain the difference between exothermic and endothermic processes.

State.

Mention the temperature at which combustion and neutralization occur.

The question asks for a statement indicating that combustion and neutralization are exothermic processes. This requires a direct statement affirming the exothermic nature of these reactions. The incorrect answers either provide irrelevant information or do not address the specific requirement of the question.

Explanation

The question asks for a statement indicating that combustion and neutralization are exothermic processes. This requires a direct statement affirming the exothermic nature of these reactions. The incorrect answers either provide irrelevant information or do not address the specific requirement of the question.

2. Apply the relationship between temperature change, enthalpy change and the classification of a reaction as endothermic or exothermic.

C. Exothermic reactions have a positive enthalpy change and endothermic reactions have a negative enthalpy change.

B. Endothermic reaction is one in which heat is given out to the environment and the temperature of the system increases.

In an exothermic reaction, heat is given out to the environmentand the temperature of the system increases. Endothermic reaction is one in which heat is takenin from environment and the temperature of the system decreases. The reaction mixture is calledthe system and anything around the system is called the surrounding or environment.
Exothermic -> a reaction which produces heat (?H has a negative value by convention, -ve)Endothermic -> a reaction which absorbs heat (?H has a positive value by convention, +ve)

A. In an exothermic reaction, heat is taken in from the environment and the temperature of the system decreases.

The correct answer describes the relationship between temperature change, enthalpy change, and the classification of reactions as endothermic or exothermic accurately.

Explanation

The correct answer describes the relationship between temperature change, enthalpy change, and the classification of reactions as endothermic or exothermic accurately.

3. From an enthalpy level diagram, how can the relative stabilities of reactants and products be deduced, and what is the sign of the enthalpy change for the reaction?

The most stable state is where all energy has been absorbed. When going to a more stable state, energy will be gained, and when going to a less stable state, energy will be released.

On an enthalpy level diagram, higher positions are more stable, therefore if the product is higher, heat is released (?H is -ve), but if it is lower, heat is gained (?H is +ve).

See notes.
The most stable state is where all energy has been released. When going to a more stable state, energy will be released, and when going to a less stable state, energy will be gained (from the surroundings). On an enthalpy level diagram, higher positions will be less stable (with more internal energy) therefore, if the product is lower, heat is released (more stable, ?H is -ve) but if it is higher, heat is gained (less stable, ?H is +ve).Formation of bonds causes an energy release (exothermic).Breaking of bonds requires energy (endothermic).

Formation of bonds requires energy release and breaking of bonds causes energy gain.

The correct answer explains that the release of energy occurs when going to a more stable state, while energy is gained when going to a less stable state. The formation of bonds releases energy, while breaking bonds requires energy.

Explanation

The correct answer explains that the release of energy occurs when going to a more stable state, while energy is gained when going to a less stable state. The formation of bonds releases energy, while breaking bonds requires energy.

4. Calculate the enthalpy change for a reaction using experimental data on temperature changes, quantities of reactants and mass of water.

Neglect the mass of water used in the reaction as it does not affect the enthalpy change calculation.

Mix reactants in an open environment to allow heat to be released easily for enthalpy change calculation.

A known mass of solution should be placed in a container, as insulated as possible, to prevent as much heat as possible from escaping. The temperature is measured continuously, the value used in the equation is the maximum change in temperature from the initial reading.The result will be a change in temperature. This can be converted into a change in heat (or energy) by using the above equation E = m x c x ?T.?-H may then be calculated for the amount of reactants present, and then this can be used to calculate for a given number of mols.

Increase the temperature of the water used in the reaction and record the change in color as an indicator of enthalpy change.

To calculate enthalpy change accurately, it is important to ensure proper insulation of the container to minimize heat loss, measure temperature changes correctly, and consider the mass of water as it affects the overall enthalpy change.

Explanation

To calculate enthalpy change accurately, it is important to ensure proper insulation of the container to minimize heat loss, measure temperature changes correctly, and consider the mass of water as it affects the overall enthalpy change.

5. 5.2.4: Evaluate the results of experiments to determine enthalpy changes.

The results of experiments to determine enthalpy changes are always 100% accurate.

Enthalpy changes can be accurately determined without accounting for experimental errors.

Students should focus only on the final result without considering experimental methods.

Students should be aware of the assumptions madeand errors due to heat loss.

When evaluating the results of experiments to determine enthalpy changes, it is important for students to consider the assumptions made during the experiment and any errors that may have occurred due to heat loss. Ignoring the experimental methods or assuming 100% accuracy in results can lead to incorrect conclusions.

Explanation

When evaluating the results of experiments to determine enthalpy changes, it is important for students to consider the assumptions made during the experiment and any errors that may have occurred due to heat loss. Ignoring the experimental methods or assuming 100% accuracy in results can lead to incorrect conclusions.

6. Explain, in terms of average bond enthalpies, why some reactions are exothermic and others are endothermic.

Reactions that release heat are endothermic, while reactions that absorb heat are exothermic.

Bond breaking needs energy and is anendothermic process. Bond making releases energy and it is an exothermic process.

The nature of the elements involved in the reaction determines whether it will be exothermic or endothermic.

Exothermic reactions always involve breaking bonds, while endothermic reactions always involve making bonds.

Endothermic reactions require energy input to break bonds, while exothermic reactions release energy when new bonds are formed. The bond enthalpies play a crucial role in determining the overall energy change in a reaction.

Explanation

Endothermic reactions require energy input to break bonds, while exothermic reactions release energy when new bonds are formed. The bond enthalpies play a crucial role in determining the overall energy change in a reaction.