Equilibrium constant Kc

This question is about equilibrium and rates.

This question is about oxides of nitrogen.

An investigation is carried out on the equilibrium system shown below.

A sealed flask containing 6.00 moles of NO₂(g) is heated to a constant temperature and allowed to reach equilibrium.

The equilibrium mixture contains 5.40 mol of NO₂(g), and the total pressure is 5.00 atm.

Determine the value of K_p and give your answer to 3 significant figures.

Include an expression for K_p and the units of K_p in your answer.

The sealed flask in (a)(i) is then heated to a higher temperature at an increased pressure. The system is allowed to reach equilibrium again.

Explain why it is difficult to predict how these changes in reaction conditions affect the amount of N₂O₄(g) formed at equilibrium.

N₂O₄ reacts fully with oxygen to form a different oxide of nitrogen, oxide A, as the only product.

Oxide A is collected and cooled to 75.0 °C at a pressure of 101 kPa.

Under these conditions, oxide A is a gas that occupies a volume of 74.0 cm³ and has a mass of 0.280 g.

Calculate the molar mass of oxide A and suggest its molecular formula.

molar mass =........ g mol

This question is about nitric acid, hydrochloric acid and sulfuric acid.

Dilute nitric acid reacts with aluminium oxide to form a solution of aluminium nitrate.

Write an equation for this reaction.

The solution contains nitrate ions, NO₃^–.

Draw a ‘dot-and-cross’ diagram for the NO₃^– ion.

Use a different symbol for the extra electron.

Balance the half-equation for the oxidation process in this reaction.

In the reduction process in this reaction, HNO₃ and H⁺ react together to form 2 oxides: X (M_r = 30) and Z (M_r = 18).

Determine the formulae of X and Z and write the half-equation for this reduction.

* Three reactions involving sulfuric acid are shown below.

Reaction 1 Dilute sulfuric acid is reacted with nickel(II) hydroxide to form a green solution.

The solvent is allowed to evaporate leaving hydrated crystals of compound D, with the percentage composition by mass: Ni, 22.33%; S, 12.20%; O, 60.87%; H, 4.60%.

Reaction 2 Concentrated sulfuric acid is reacted with hydrogen bromide, HBr, to form three products:

• an element which exists as diatomic molecules

• a gaseous compound E

• a liquid.

At RTP, 1.00 dm³ of compound E has a mass of 2.67 g.

Reaction 3 Concentrated sulfuric acid acts as a catalyst when 2-hydroxypropanoic acid reacts to form compound F (M_r = 144).

In this reaction, 2 mol of 2-hydroxypropanoic acid forms 1 mol of compound F and 2 mol of water.

Identify compounds D, E and F and construct equations for the reactions.

Show structures for any organic compounds.

This question is about equilibria involving hydrogen.

* Hydrogen is used industrially to manufacture ammonia.

The equilibrium is shown below.

1.20 mol N₂(g) is mixed with 3.60 mol H₂(g) in a 8.00 dm³ container.

The mixture is heated to 550 °C with an iron catalyst and allowed to reach equilibrium.

The equilibrium mixture contains 0.160 mol of NH₃.

Determine the equilibrium constant K_c for Equilibrium 20.1, and explain why the operational conditions used by industry may be different from those required for a maximum equilibrium

yield of ammonia.

In industry, hydrogen is also used to reduce the iron oxide Fe₃O₄ as shown in Equilibrium 20.2.

The reaction is carried out at 500 °C.

When the temperature is decreased, the value of K_p decreases.

Determine whether the forward reaction is exothermic or endothermic. Explain your answer.

Two students are discussing the effect of pressure on the equilibrium position of Equilibrium 20.2.

Student 1 says:

“There are more moles of products than reactants, so increasing the pressure will shift the equilibrium to the left hand side.”

Student 2 disagrees.

Determine which student is correct. Justify your answer.

Sulfuric acid is an important chemical used to make detergents, fertilisers and dyes. It is manufactured in a multi-step process.

In the first step of the manufacture of sulfuric acid, sulfur dioxide, SO₂, can be made from the combustion of hydrogen sulfide, H₂S, shown in Reaction 1.

Explain why the enthalpy change for Reaction 1 has a negative value.

Use ideas about enthalpy changes associated with bond breaking and bond making.

Some standard entropy values are given below.

Substance	H2S(g)	O2(g)	SO2(g)	H2O(l)
S / J K−1 mol−1	206	205	248	70

Using calculations, explain whether Reaction 1 is feasible at 20 °C.

Calculations

Explanation for feasible or non feasible........

Write an expression for K_p for Equilibrium 1.

Include the units.

Determine the value of K_p for Equilibrium 1 at 1000 K.

Show all your working.

Give your answer to 3 significant figures.

The chemist repeats the experiment in (b) at a different temperature.

The chemist finds that the value of K_p is greater than the answer to (b)(ii).

Explain whether the temperature in the second experiment is higher or lower than 1000 K.

Vanadium(V) oxide, V₂O₅(s), is used as a catalyst in equilibrium 1.

Explain whether vanadium(V) oxide is acting as a homogeneous or heterogeneous catalyst.

Nitrogen monoxide, NO, and oxygen, O₂, react to form nitrogen dioxide, NO₂, in the reversible reaction shown in equilibrium 18.1.

Write an expression for K_c for this equilibrium and state the units.

K_c =

A chemist mixes together nitrogen and oxygen and pressurises the gases so that their total gas volume is 4.0 dm³.

• The mixture is allowed to reach equilibrium at constant temperature and volume.

• The equilibrium mixture contains 0.40 mol NO and 0.80 mol O₂.

• Under these conditions, the numerical value of K_c is 45.

Calculate the amount, in mol, of NO₂ in the equilibrium mixture.

The values of K_p for equilibrium 18.1 at 298 K and 1000 K are shown below.

Predict, with a reason, whether the forward reaction is exothermic or endothermic.

The chemist increases the pressure of the equilibrium mixture at the same temperature.

State, and explain in terms of K_p, how you would expect the equilibrium position to change.

A student carries out two experiments in the laboratory based on succinic acid (butanedioic acid), (CH₂COOH)₂.

Succinic acid is esterified by ethanol, C₂H₅OH, in the presence of an acid catalyst to form an equilibrium mixture.

The equilibrium constant, K_c, for this equilibrium can be calculated using the amounts, in moles, of the components in the equilibrium mixture, using expression 5.1.

A student carries out an experiment to determine the value of K_c for this equilibrium.

• The student mixes together 0.0500 mol of succinic acid and 0.150 mol of ethanol, with a small amount of an acid catalyst.

• The mixture is allowed to reach equilibrium.

• The student determines that 0.0200 mol of succinic acid are present in the equilibrium mixture.

Which technique could be used to determine the equilibrium amount of succinic acid?

Write the equation for the equilibrium reaction that takes place.

Draw the skeletal formula of the ester present in the equilibrium mixture.

K_c is the equilibrium constant in terms of equilibrium concentrations.

Why can expression 5.1 be used to calculate K_c for this equilibrium?

Calculate the value of K_c for this reaction.

Show your working.