The effect of changing conditions on equilibrium

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 some gas mixtures at equilibrium.

This reaction can be used to make hydrogen.

A mixture of 2.00 mol of H₂O(g) and 2.00 mol of CO(g) is allowed to reach equilibrium at a constant temperature in a 20 dm³ container. At equilibrium, there are 0.92 mol of H₂(g).

Calculate the mole fraction of H₂(g) in the equilibrium mixture.

State why the equilibrium constant (K_p) for this reaction has no units.

The temperature of the equilibrium mixture formed in Question 04.1 is increased.

How does the amount of H₂(g) change when the new position of equilibrium is reached?

Tick (✓) one box.

Ethanol can be made from ethene and steam.

Table 2 shows the mole fractions of each of the gases in an equilibrium mixture at 6000 kPa

Give an expression for K_p for this reaction.

Calculate the value of K_p at 6000 kPa

State the units.

State the effect, if any, of an increase in volume of the container on the value of K_p for this reaction at a constant temperature.

This question is about an equilibrium.

A 25.0 cm³ sample of a solution of P is added to a 20.0 cm³ sample of a solution of Q The mixture is allowed to reach equilibrium.

The amounts in the equilibrium mixture are

P = 0.0145 mol Q = 0.0275 mol R = 0.0115 mol S = 0.0345 mol

Calculate the amount, in moles, of P before the reaction with Q.

Use your answer to calculate the concentration, in mol dm^–3, of P in the

Give the expression for the equilibrium constant, K_c

Calculate the value of K_c and deduce its units.

Explain why the amount of S increases when water is added to the equilibrium mixture.

Which statement about the industrial production of ethanol from ethene at 300 °C is correct?

This question is about equilibria.

Give two features of a reaction in dynamic equilibrium.

A gas-phase reaction is at equilibrium. When the pressure is increased the yield of product decreases.

State what can be deduced about the chemical equation for this equilibrium.

Carbon monoxide and hydrogen react to form methanol.

0.430 mol of carbon monoxide is mixed with 0.860 mol of hydrogen. At equilibrium, the total pressure in the flask is 250 kPa and the mixture contains 0.110 mol of methanol.

Calculate the amount, in moles, of carbon monoxide present at equilibrium.

Calculate the partial pressure, in kPa, of carbon monoxide in this equilibrium mixture.

Give an expression for the equilibrium constant (K_p) for this reaction.

A different mixture of carbon monoxide and hydrogen is left to reach equilibrium at a temperature T.

Some data for this equilibrium are shown in Table 1.

Calculate the partial pressure, in kPa, of hydrogen in this equilibrium mixture.

Use the K_p value from Table 1 to calculate a value for K_p for the following reaction at temperature T.

Give the units for K_p

Tetrafluoroethene is made from chlorodifluoromethane in this reversible reaction.

A 2.00 mol sample of CHClF₂ is placed in a container of volume 23.2 dm³ and heated. When equilibrium is reached, the mixture contains 0.270 mol of CHClF₂

Calculate the amount, in moles, of C₂F₄ and of HCl in the equilibrium mixture.

Give an expression for K_c for this equilibrium.

Calculate a value for K_c

Give its units.

State and explain the effect of using a higher temperature on the equilibrium yield of tetrafluoroethene.

Chemists provided evidence that was used to support a ban on the use of chlorodifluoromethane as a refrigerant.

Many refrigerators now use pentane as a refrigerant.

State the environmental problem that chlorodifluoromethane can cause.

Give one reason why pentane does not cause this problem.

Environmental problem

This question is about the equilibrium

State and explain the effect, if any, of a decrease in overall pressure on the

Calculate the partial pressure, in kPa, of SO₂ in this equilibrium mixture.

Table 4 shows the partial pressures of the gases at equilibrium.

Give an expression for the equilibrium constant (K_p) for this reaction.

Calculate the value of the equilibrium constant for this reaction and give its units.

What is the effect on the value of K_p if the pressure of this equilibrium mixture is increased at a constant temperature?

Tick (✓) one box.

This question is about pH.

Pure water dissociates slightly.

The ionic product of water, K_w = [H⁺][OH⁻]

Explain why [H₂O] is not shown in the K_w expression.

Table 5 shows how K_w varies with temperature.

Explain why the value of K_w increases as the temperature increases.

Give the expression for pH.

Calculate the pH of pure water at 50 °C Give your answer to 2 decimal places.

Explain why water is neutral at 50 °C

Calculation

A pH meter is calibrated using a calibration graph. To create the calibration, the pH meter is used to measure the pH of separate solutions, each with a known, accurate pH.

Figure 3 shows the calibration graph.

Use Figure 3 to give the true pH value when the pH meter reading is 5.6

Suggest why the pH probe is washed with distilled water between each of the calibration measurements.

The calibrated pH meter is used to monitor the pH during a titration of hydrochloric acid with sodium hydroxide.

Explain why the volume of sodium hydroxide solution added between each pH measurement is smaller as the end point of the titration is approached.

Table 6 shows data about some indicators.

The student plans to do the titration again using one of the indicators in Table 6 to determine the end point.

State why all three of the indicators in Table 6 are suitable for this titration.

36.25 cm³ of 0.200 mol dm^–3 sodium hydroxide solution are added to 25.00 cm³ of 0.150 mol dm^–3 hydrochloric acid.

Calculate the pH of the final solution at 25 ºC

Which statement about the addition of a catalyst to an equilibrium mixture is correct?

Methanol can be manufactured in a reversible reaction as shown.

Figure 3 shows how the partial pressures change with time at a constant temperature.

Draw a cross (x) on the appropriate axis of Figure 3 when the mixture reaches equilibrium.

At equilibrium the mixture contains 0.120 mol of carbon monoxide.

Calculate the partial pressure, in kPa, of hydrogen in the equilibrium mixture.

Give an expression for the equilibrium constant (K_p) for this reaction.

State the units.

Some more carbon monoxide is added to the mixture in Question 06.2. The new mixture is allowed to reach equilibrium at temperature T.

State the effect, if any, on the partial pressure of methanol and on the value of K_p

Effect on partial pressure of methanol

State the effect, if any, of the addition of a catalyst on the value of K_p for this equilibrium. Explain your answer.

This question is about sulfuric acid and its salts.

Draw the displayed formula of a molecule of H₂SO₄

In aqueous solution, sulfuric acid acts as a strong acid. The H₂SO₄ dissociates to form HSO₄ ions and H⁺ ions.

The HSO₄ ions act as a weak acid and dissociate to form SO₄² ions and H⁺ ions.

Give an equation to show each stage in the dissociation of sulfuric acid in aqueous solution.

Include appropriate arrows in your equations.

A student is required to make 250 cm³ of an aqueous solution that contains an accurately measured mass of sodium hydrogensulfate (NaHSO₄).

Describe the method that the student should use to make this solution.

A solution that contains 605 mg of NaHSO₄ in 100 cm³ of solution has a pH of 1.72

Calculate the value of K_a for the hydrogensulfate ion (HSO₄) that is behaving as a weak acid. Give your answer to three significant figures.

Some sodium sulfate is dissolved in a sample of the solution from question 02.4.

Explain why this increases the pH of the solution.

Which change leads to a higher concentration of SO₃ in this equilibrium mixture?

Nitrogen reacts with hydrogen in this exothermic reaction

Which change increases the equilibrium yield of ammonia but has no effect on the value of the equilibrium constant K_p?

For this reaction at equilibrium, which combination of temperature and pressure would give the greatest equilibrium yield of products?