Bond energy calculations

Nitrogen dioxide gas is formed when magnesium nitrate is heated.

Table 4 shows some thermodynamic data.

Give the standard conditions indicated by the symbol in Δ_f and

Use the equation and the data in Table 4 to calculate the temperature at which this reaction becomes feasible.

Nitrogen dioxide can also be produced in a reaction between ammonia and oxygen.

Table 5 shows some bond enthalpy values.

Assume that the bonds between N and O in NO₂ are the same.

Calculate the mean bond enthalpy, in kJ mol^–1, for a bond between N and O in NO₂

An alloy of platinum and rhodium is used as a catalyst in the reaction.

What type of catalyst is this?

Some ammonia and oxygen are reacted and the mixture is left to reach equilibrium at a fixed temperature.

Explain why increasing the temperature of this equilibrium mixture decreases the mole fraction of NO₂ in the equilibrium mixture.

This question is about enthalpy of combustion.

Limonene is found in the skin of citrus fruits.

Figure 6 shows a diagram of the apparatus used in an experiment to determine a value for the enthalpy of combustion of limonene.

When 1.31 g of limonene are burned, the temperature of the 60.0 g of water in the copper calorimeter increases by 52.1 °C

The specific heat capacity of water is 4.18 J K^–1 g^–1

Calculate a value for the enthalpy of combustion, in kJ mol^–1, of limonene (C₁₀H₁₆).

Table 3 shows values, obtained by different methods, for the enthalpy of combustion of a different liquid hydrocarbon.

Suggest reasons for the differences between the values obtained by each of Methods 2 and 3, and the value obtained by Method 1 in Table 3.

This question is about biofuels.

Palmitic acid, CH₃(CH₂)₁₄COOH, can be made by hydrolysis of the triester in palm oil under acidic conditions. Palmitic acid can be used as a biofuel.

Complete the equation for the hydrolysis of the triester in palm oil under acidic conditions.

Palmitic acid burns in air.

In a calorimetry experiment, combustion of 387 mg of palmitic acid increases the temperature of 0.150 kg of water from 23.9 °C to 37.5 °C

Calculate a value, in kJ mol^–1, for the enthalpy of combustion of palmitic acid in this experiment. Give your answer to the appropriate number of significant figures.

The specific heat capacity of water is 4.18 J K^–1 g^–1

State how the value calculated in Question 08.2 is likely to differ from data book values.

Give one reason, other than heat loss, for this difference.

A sample of a different biofuel, made from sewage sludge, is found to contain 37.08% carbon, 5.15% hydrogen and 24.72% oxygen by mass. The rest of the sample is sulfur.

Calculate the empirical formula of this biofuel.

Empirical formula

Complete combustion of the biofuel made from sewage sludge produces the greenhouse gas carbon dioxide.

Suggest one other possible environmental problem with the complete combustion of this biofuel.

State the formula of the pollutant responsible for this problem.

Environmental problem

Ethanol is a biofuel that can be produced by the fermentation of glucose.

Glucose has the structural formula shown.

Table 3 shows some mean bond enthalpy values.

Use the equation and the data in Table 3 to calculate an approximate value of Δ H for the fermentation of glucose. For this calculation you should assume that all the substances are in the gaseous state.

The carbon dioxide produced from fermentation can be reacted with steam to make more ethanol.

The equation for this reaction is

Table 4 shows some standard enthalpies of formation.

Use the data in Table 4 to calculate a standard enthalpy change value for this reaction.

This question is about hydrogen peroxide, H₂O₂

The half-equation for the oxidation of hydrogen peroxide is

Hair bleach solution contains hydrogen peroxide.

A sample of hair bleach solution is diluted with water. The concentration of hydrogen peroxide in the diluted solution is 5.00% of that in the original solution. A 25.0 cm³ sample of the diluted hair bleach solution is acidified with dilute sulfuric acid. This acidified sample is titrated with 0.0200 mol dm⁻³ potassium manganate(VII) solution. The reaction is complete when 35.85 cm³ of the potassium manganate(VII) solution are added.

Give an ionic equation for the reaction between potassium manganate(VII) and acidified hydrogen peroxide.

Calculate the concentration, in mol dm^–3, of hydrogen peroxide in the original hair bleach solution.

(If you were unable to write an equation for the reaction you may assume that the mole ratio of potassium manganate(VII) to hydrogen peroxide is 3:4 This is not the correct mole ratio.)

State why an indicator is not added in this titration.

Give the oxidation state of oxygen in hydrogen peroxide.

Hydrogen peroxide decomposes to form water and oxygen.

Give an equation for this reaction.

Calculate the amount, in moles, of hydrogen peroxide that would be needed to produce 185 cm³ of oxygen gas at 100 kPa and 298 K

The gas constant, R = 8.31 J K⁻¹ mol⁻¹

Equation

Hydrazine (N₂H₄) is used as a rocket fuel that is oxidised by hydrogen peroxide. The equation for this reaction in the gas phase is

The enthalpy change for this reaction, ∆ H = – 789 kJ mol

Table 3 shows some mean bond enthalpy values.

Define the term mean bond enthalpy.

Use the equation and the data in Table 3 to calculate a value for the O–O bond enthalpy in hydrogen peroxide.

Use Figure 3 and the data shown in Table 1 to calculate ΔH₂

A mixture of concentrated nitric acid and concentrated sulfuric acid reacts with benzene.

Figure 4 shows the incomplete mechanism for this reaction.

Name the mechanism.

Complete the mechanism in Figure 4 by adding

• any lone pairs of electrons involved in each step

• two curly arrows in step 1

• a curly arrow in step 2

• a curly arrow in step 3

• a curly arrow in step 4.

Name of mechanism