Edexcel Combined Science C3 - Physical Chemistry

When natural gas burns in air, the reaction is:

• Endothermic, because heat is given out

• Endothermic, because heat is taken in

• Exothermic, because heat is given out

• Exothermic, because heat is taken in

The best way to explain why chemical reactions involve changing energy is:

• Any reaction must involve energy

• The law of conservation of energy means that reactions must involve energy

• Chemical reactions involve breaking and making bonds, and different bonds have different energies

The diagram shows the energy levels for a reaction. This reaction....

• is endothermic, the products have more energy than the reactants so energy must have been taken in

• is exothermic, the products have less energy than the reactants so energy must have been released

• could be either exothermic or endothermic, it is not possible to say

In an experiment, a scientist adds table salt (Sodium Chloride, NaCl) to a beaker of water. She first measures the temperature of the water.

After the salt has dissolved, she re-measures the temperature.

What would you expect her to see?

• The temperature will be the same

• The temperature will have decreased because the reaction (dissolving in water) is endothermic so energy is taken from the water

• The temperature will have increased because the reaction (dissolving in water) is exothermic so energy is released to the water

In the chart, the distance from the initial energy to the peak is --

• the energy change

• proof of an exothermic reaction

• the activation energy

• 100 x 40 x 5 = 20,000J

• 100 x 40 x 5 = 20,000W

• 0.1 x 40 x 5 = 20K

• 0.1 x 40 x 5 = 20J

The rate reaction of a chemical change can be increased by:

[Tick all that apply]

• Increasing the surface area of a solid reactant

• Decreasing the concentration of a reactant in solution

• Using a catalyst (although this only works for some reactions)

• Increasing the temperature of the reactants

• Increasing the pressure of a gaseous reactant

In a certain reaction, a chemist uses 5g of Nickel powder as a catalyst.

At the completion of the reaction, how much Nickel powder will remain?

• Less than 5g

• 5g

• More than 5g

• It depends on the specifics of the reaction