Exothermic & Endothermic Reactions (Cambridge (CIE) IGCSE Co-ordinated Sciences (Double Award): Chemistry): Exam Questions

The first three elements in Period 6 of the Periodic Table of the Elements are caesium, barium and lanthanum.

How many more protons, electrons and neutrons are there in one atom of lanthanum than in one atom of caesium. Use your copy of the Periodic Table of the Elements to help you.

number of protons ................................................

number of electrons ................................................

number of neutrons ................................................

Extended tier only

All three metals can be obtained by the electrolysis of a molten halide. The electrolysis of the aqueous halides does not produce the metal.

i) Complete the equation for the reduction of lanthanum ions at the negative electrode (cathode).

La³⁺ + ................ → ................

ii) Name the three products formed by the electrolysis of aqueous caesium bromide. 

All three metals react with cold water. Complete the word equation for these reactions.

metal + water → ................................. + .............................

Barium chloride is an ionic compound. Draw a diagram that shows the formula of the compound, the charges on the ions and gives the arrangement of the valency electrons around the negative ion.

The electron distribution of a barium atom is 2.8.18.18.8.2

Use x to represent an electron from a barium atom. Use o to represent an electron from a chlorine atom.

Extended tier only

Describe, by means of a simple diagram, the lattice structure of an ionic compound, such as caesium chloride.

Extended tier only

The reactions of these metals with oxygen are exothermic.

2Ba (s) + O₂ (g) → 2BaO (s)

i) Give an example of bond forming in this reaction.

[1]

ii) Explain using the idea of bond breaking and forming why this reaction is exothermic.

[3] 

Thermal energy is released to the surroundings when hydrogen is burnt.

State the name of the type of reaction which transfers heat to the surroundings.

Extended tier only

Ammonia, NH₃, is used to produce nitric acid, HNO₃. This happens in a three-stage process.

The reaction in stage 3 is exothermic.

4NO₂ + 2H₂O + O₂ → 4HNO₃

Complete the energy level diagram for this reaction. Include an arrow that clearly shows the energy change during the reaction.

Iodine reacts with aqueous sodium thiosulfate, Na₂S₂O₃.

Balance the chemical equation for this reaction.

Extended tier only

The energy level diagram for this reaction is shown. 

Explain how this diagram shows that the reaction is exothermic.

Heat is given out when iron reacts with sulfuric acid.

What term describes a reaction which gives out heat?

The reaction of iron(II) carbonate with hydrochloric acid is exothermic.

What is meant by the term exothermic?

Extended tier only

The reaction between ethanoic acid and ethanol is exothermic.

Draw an energy level diagram for this reaction.

On your diagram label:

• the reactants and products

• the energy change of the reaction, ∆H.

Extended tier only

Period 3 contains the elements sodium to argon. This question asks about the chemistry of each of the Period 3 elements or their compounds.

Sodium nitrate is a white crystalline solid. When heated it melts and the following reaction occurs.

2NaNO₃ (l) → 2NaNO₂ (l) + O₂ (g)

A 3.40 g sample of sodium nitrate is heated.

Calculate the

• number of moles of NaNO₃ used,

.................................. mol

• number of moles of O₂ formed,

.................................. mol

• volume of O₂ formed, in dm³ (measured at r.t.p.).

.................................. dm³

Magnesium reacts slowly with warm water to form a base, magnesium hydroxide.

 i) Explain what is meant by the term base.

[1]

ii) Write a chemical equation for the reaction between magnesium and warm water.

[2]

Extended tier only

Aluminium oxide is amphoteric. It is insoluble in water.

Describe experiments to show that aluminium oxide is amphoteric.

Extended tier only

Calcium phosphate is used in fertilisers. The bonding in calcium phosphate is ionic. Calcium phosphate contains the phosphate ion, PO₄^3–.

i) What is ionic bonding?

[2]

 ii) Deduce the formula of calcium phosphate.

[1]

Sulfur tetrafluoride, SF₄, can be made by combining gaseous sulfur with fluorine.

 S (g) + 2F₂ (g) → SF₄ (g)

The reaction is exothermic.

Complete the energy level diagram for this reaction. Include an arrow which clearly shows the energy change during the reaction.

Chlorine and compounds of chlorine are important in water treatment and in laboratory testing for water.

i) Chlorine is added to water to make the water safe to drink.

 Explain why adding chlorine makes water safe to drink.

[1]

ii) A compound of chlorine is used in the laboratory to test for the presence of water.

 Name the compound of chlorine used in this test and describe the colour change seen in a positive result of this test.

 name of compound ..................................................

 colour change from .............................. to ..............................

[3]

Argon is an unreactive noble gas. Explain why argon is unreactive.

Extended tier only

Three of the factors that can influence the rate of a chemical reaction are:

• physical state of the reactants

• light

• the presence of a catalyst

The first recorded dust explosion was in a flour mill in Italy in 1785. Flour contains carbohydrates. Explosions are very fast exothermic reactions.

i) Use the collision theory to explain why the reaction between the particles of flour and the oxygen in the air is very fast.

[2]

ii) Write a word equation for this exothermic reaction.

[1] 

The decomposition of silver(I) bromide is the basis of film photography. The equation for this decomposition is:

This reaction is photochemical.

A piece of white paper was coated with silver(I) bromide and the following experiment was carried out.

Explain the results.

Extended tier only

Chemical reactions are always accompanied by an energy change.

Aluminium is extracted by the electrolysis of a molten mixture which contains aluminium oxide, Al₂O₃. This decomposes to form aluminium at the negative electrode and oxygen at the positive electrode.

i) Write an ionic equation for the reaction at the negative electrode.

[2]

ii) Complete the ionic equation for the reaction at the positive electrode.

2O^2– → ....... + .......

[2]

iii) Is the reaction exothermic or endothermic? Explain your answer.

[1]

Extended tier only

The cell shown below can be used to determine the order of reactivity of metals.

i) Is the reaction in the cell exothermic or endothermic? Explain your answer.

[1]

ii) Explain why the mass of the magnesium electrode decreases and the mass of the copper electrode increases.

[2]

iii) How could you use this cell to determine which is the more reactive metal, magnesium or manganese?

[2] 

Extended tier only

The combustion of propane, C₃H₈, is exothermic.

Give an equation for the complete combustion of propane.

Draw a dot cross diagram for hydrazine, N₂H₄. 

Use x to represent electrons from nitrogen atoms

Use o to represent electrons from hydrogen atoms

Extended tier only

When nitrogen and oxygen are heated to very high temperatures, they combine to form nitrogen monoxide and a lot of heat is absorbed in this reaction. 

Complete the reaction pathway diagram to show the formation of nitrogen monoxide from nitrogen and oxygen.