Bond energy calculations

Hydrazine (N₂H₄) is a compound of nitrogen and hydrogen.

Scientists are researching the use of hydrazine in fuel cells.

Table 2 gives some information about the use of hydrogen and hydrazine in fuel cells.

Evaluate the use of hydrazine instead of hydrogen in a fuel cell.

Figure 6 shows a model of the hydrazine molecule.

Complete the dot and cross diagram for hydrazine in Figure 7.

Show the outer shell electrons only.

Give one advantage of the ball and stick model in Figure 6 compared to the dot and cross diagram.

Figure 8 shows the displayed formula equation for the reaction of hydrazine with oxygen.

The reaction is exothermic.

The energy released forming new bonds is 581 kJ/mol greater than the energy needed to break existing bonds.

Table 3 shows some bond energies.

Calculate the bond energy (X) of the bond.

This question is about propane (C₃H₈).

Figure 7 shows the displayed structural formula of propane.

Explain why propane has a low boiling point.

Propane reacts with oxygen to produce carbon dioxide and water.

The reaction is exothermic.

Figure 8 shows four reaction profiles.

Which is the correct reaction profile and labels for the reaction between propane and oxygen?

Tick () one box.

Figure 9 shows the displayed formula equation for the reaction between propane and oxygen.

The overall energy change of this exothermic reaction is 2219 kJ/mol.

Table 4 shows the bond energies of the bonds in the reaction.

Calculate the bond energy of the C — H bond (X).

This question is about hydrogen and compounds of hydrogen. Figure 3 shows the displayed formulae for the reaction between hydrogen and chlorine.

Figure 3

Table 4 shows the bond energies.

Which expression shows how to calculate the overall energy change for the reaction in Figure 3 ? Use Table 4. Tick (✓) one box.

The reaction between hydrogen and chlorine is exothermic.

Explain why this reaction releases energy to the surroundings.

Figure 4 shows part of a reaction profile for the reaction between hydrogen and chlorine. Complete the reaction profile in Figure 4. You should:

• label the activation energy

• label the overall energy change.

Draw a dot and cross diagram for a molecule of hydrogen chloride (HC l). Show the outer shell electrons only.

Figure 5 represents molecules of methane and of poly(ethene).

Methane is a gas at room temperature but poly(ethene) is a solid at room temperature.

Explain why methane and poly(ethene) exist in different states at room temperature.

This question is about the reaction between hydrogen sulfide (H₂S) and oxygen. The equation for the reaction is:

What does H₂O(g) represent?

Calculate the volume of oxygen required to react with 50 cm³ of hydrogen sulfide.

Figure 6 shows part of the reaction profile for the reaction. The reaction is exothermic. Complete Figure 6. You should:

• complete the profile line

• label the activation energy

• label the overall energy change.

Figure 7 shows the displayed formula equation for the reaction of hydrogen sulfide with oxygen.

Figure 7

Table 5 shows some of the bond energies.

In the reaction the energy released forming new bonds is 1034 kJ/mol greater than the energy needed to break existing bonds. Calculate the bond energy X for the bond. Use Figure 7 and Table 5.

This question is about ammonia, NH₃

Complete the dot and cross diagram for the ammonia molecule shown in Figure 6. Show only the electrons in the outer shell of each atom.

Give one limitation of using a dot and cross diagram to represent an ammonia molecule.

Explain why ammonia has a low boiling point. You should refer to structure and bonding in your answer.

Ammonia reacts with oxygen in the presence of a metal oxide catalyst to produce nitrogen and water.

Which metal oxide is most likely to be a catalyst for this reaction? Tick (✓) one box.

Figure 7 shows the displayed formula equation for the reaction.

Table 3 shows some bond energies.

Calculate the overall energy change for the reaction. Use Figure 7 and Table 3.

Explain why the reaction between ammonia and oxygen is exothermic. Use values from your calculation in Question 05.5

Figure 8 shows the reaction profile for the reaction between ammonia and oxygen. Complete Figure 8 by labelling the:

• activation energy

• overall energy change.

This question is about Group 7 elements. Chlorine is more reactive than iodine.

Name the products formed when chlorine solution reacts with potassium iodide solution.

Explain why chlorine is more reactive than iodine.

Chlorine reacts with hydrogen to form hydrogen chloride. Explain why hydrogen chloride is a gas at room temperature. Answer in terms of structure and bonding.

Bromine reacts with methane in sunlight. Figure 9 shows the displayed formulae for the reaction of bromine with methane.

Table 3 shows the bond energies and the overall energy change in the reaction.

Calculate the bond energy X for the C^___Br bond. Use Figure 9 and Table 3.