Equilibrium constant Kc

50.0 cm³ of 0.015 mol dm^–3 Fe₂(SO₄)₃(aq) are mixed with 50.0 cm³ of

The mixture is left for several hours until equilibrium is reached.

A sample of the equilibrium mixture is titrated to determine the amount of I^–(aq) in the equilibrium mixture.

Give the expression for the equilibrium constant, K_c, for the equilibrium.

Before the titration, the sample is ‘quenched’ by adding 50 cm³ of ice-cold water.

Suggest why the sample is ‘quenched’ in this way before the titration. Explain your answer.

The amount of I^–(aq) in the equilibrium mixture is found to be 3.00 × 10^–4 mol

Calculate the value of K_c at 40 °C for the equilibrium.

Assume that the total volume of the mixture remains constant at 100 cm³

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 catalysts used in reactions at equilibrium, at a constant temperature, is correct?

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 equilibrium.

1 mol of a diester with molecular formula C₇H₁₂O₄ is added to 1 mol of water in the presence of a small amount of catalyst. The mixture is left to reach equilibrium at a constant temperature.

At equilibrium, mol of ethanoic acid are present in the mixture.

Complete Table 2 by deducing the amounts, in terms of , of the diester, water and diol present in the equilibrium mixture.

Deduce the structure of the diester in Question 05.1

A new equilibrium mixture of the substances from Question 05.1 is prepared at a different temperature.

Table 3 shows the amount of each substance in this new equilibrium mixture.

The value of the equilibrium constant, K_c is 0.161 at this temperature.

Calculate the amount of water, in mol, in this new equilibrium mixture. Show your working.

A and B react together to form an equilibrium mixture.

An aqueous solution containing 0.25 mol of A is added to an aqueous solution containing 0.25 mol of B.

When equilibrium is reached, the mixture contains 0.015 mol of C.

Calculate the amount of A and the amount of B, in moles, in the equilibrium mixture.

At a different temperature, another equilibrium mixture contains 0.30 mol of A, 0.25 mol of B and 0.020 mol of C in 350 cm³ of solution.

Calculate the value of the equilibrium constant K_c

When an excess of water is added to chloroethanal, an equilibrium mixture is formed.

An expression for an equilibrium constant (K) for the reaction under these conditions is

Suggest why an expression for K can be written without the concentration of water.

Distilled water is added to 4.71 g of chloroethanal (M_r = 78.5) to make 50.0 cm³ of solution. The mixture is allowed to reach equilibrium.

The value of the equilibrium constant (K) is 37.0

Calculate the equilibrium concentration, in mol dm^–3, of ClCH₂CH(OH)₂

When an excess of water is added to ethanal a similar nucleophilic addition reaction occurs.

Suggest why this reaction is slower than the reaction in Question 09.5.

Draw a structural formula for the diester C₆H₁₀O₄

A small amount of catalyst was added to a mixture of 0.470 mol of ethanoic acid and 0.205 mol of ethane-1,2-diol.

The mixture was left to reach equilibrium at a constant temperature.

Space for working

Write an expression for the equilibrium constant, K_c, for the reaction.

The total volume of the mixture does not need to be measured to allow a correct value for K_c to be calculated.

Justify this statement.

Expression

A different mixture of ethanoic acid, ethane-1,2-diol and water was prepared and left to reach equilibrium at a different temperature from the experiment in Question 5.2

The amounts present in the new equilibrium mixture are shown in Table 2.

The value of K_c was 6.45 at this different temperature.

Use this value and the data in Table 2 to calculate the amount, in mol, of ethanoic acid present in the new equilibrium mixture. Give your answer to the appropriate number of significant figures.

Amount of ethanoic acid
mol