IGCSE Energetics

A student adds a small amount of ammonium chloride to a beaker of water. The temperature of the water decreases from 21⁰C to 17⁰C.

Which type of reaction has occurred and why?

• exothermic, because heat is released

• exothermic, because heat is absorbed

• endothermic, because heat is released

• endothermic, because heat is absorbed

Which of the following processes is endothermic?

• reacting sodium with water

• the use of petrol in an engine

• distilling crude oil

• burning fossil fuels

The energy level diagram below shows the relative energies of the reactants and products in a reaction. (attached)

Which correctly describes the type of reaction and corresponding energy change?

• endothermic, because heat is released

• endothermic, because heat is absorbed

• exothermic, because heat is released

• exothermic, because heat is absorbed

Calcium and hydrochloric acid react to produce calcium chloride and hydrogen gas.

The energy level diagram for the reaction is shown below. (attached)

Which statement about this reaction is not correct?

• The temperature of the surroundings increases

• The reaction is endothermic

• The products have less energy than the reactants

• Energy is released during the reaction

In all chemical reactions, bonds in the reactant species are broken and new bonds are formed in the products.

Which statement is correct?

• Bond breaking requires energy and is thus an exothermic process

• Bond breaking requires energy and is thus an endothermic process

• Bond energy releases energy and is thus an exothermic process

• Bond breaking releases energy and is thus an endothermic process

Chlorine and ethane react together in an exothermic reaction to produce chloroetane and hydrogen chloride.

The equation for the reaction is shown below.

C₂H₆ + Cl₂ --> C₂H₅Cl + HCl

The table shows the relevant bond energies. (attached)

What is the energy change for the reaction between chlorine and ethane?

• -120 kJ/mol

• -1020 kJ/mol

• +120 kJ/mol

• +1020 kJ/mol

The production of ammonia involves the exothermic reaction between nitrogen and hydrogen.

The equation for the reaction is shown.

N₂ + 3H₂ --> 2NH₃

The table shows the bond energies. (attached)

What is the energy released during the reaction?

• -230 kJ/mol

• -1025 kJ/mol

• -87 kJ/mol

• +87 kJ/mol

Chlorine and hydrogen react in an exothermic reaction producing hydrogen chloride.

Cl₂ + H₂ --> 2 HCl

The table shows some of the bond energies involved. (attached)

The total energy change for this reaction is -184 kJ/mol.

What is the energy for Cl-Cl bond?

• -170 kJ/mol

• +240 kJ/mol

• +170 kJ/mol

• -240 kJ/mol

An energy level diagram is shown. (attached)

Which row is correct for the points labelled 1, 2 and 3?

• 1: activation energy

  2: energy change

  3: reactants

• 1: energy change

  2: activation energy

  3: products

• 1: energy change

  2: activation energy

  3: reactants

• 1: activation energy

  2: energy change

  3: products

Methane combusts in oxygen as shown producing an energy change of -890 kJ/mol.

CH₄ + 2O₂ --> CO₂ + 2H₂O

The table shows some of the bond energies involved (attached).

What is the energy of C=O bond?

• -155 kJ/mol

• +333 kJ/mol

• -840 kJ/mol

• +841 kJ/mol