Hess's law

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 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 thermodynamics. Consider the reaction shown.

Table 7 shows some thermodynamic data.

Explain why the standard entropy value for carbon dioxide is greater than that for carbon.

State the temperature at which the standard entropy of aluminium is 0 J K^–1 mol^–1

Use the equation and the data in Table 7 to calculate the minimum temperature, in K, at which this reaction becomes feasible.

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

Methanol is formed when carbon dioxide and hydrogen react.

Table 5 contains enthalpy of formation and entropy data for these substances.

Use the equation and the data in Table 5 to calculate the Gibbs free-energy change (ΔG), in kJ mol^–1, for this reaction at 890 K

Figure 4 shows how the Gibbs free-energy change varies with temperature in a different gas phase reaction.

The straight line graph for this gas phase reaction has been extrapolated to zero Kelvin.

Use the values of the intercept and gradient from the graph in Figure 4 to calculate the enthalpy change (ΔH), in kJ mol^–1, and the entropy change (ΔS), in J K^–1 mol^–1, for this reaction.

State what Figure 4 shows about the feasibility of the reaction.

Nitrogen dioxide is produced from ammonia and air as shown in these equations

What is the enthalpy change (in kJ mol^–1) for the following reaction?