CIE Chemistry (US-0439): Specimen Questions with Answers 108 - 109 of 240

Question number: 108

Short Answer Question▾

Write in Short

One of the factors which determine the reaction rate of solids is particle size.

An explosion is a very fast exothermic reaction. This causes a large and sudden increase in temperature.

Explain each of the following in terms of collisions between reacting particles.

Why is the reaction between finely powdered aluminum and air very fast?


Because it is Highly flammable. Ignites spontaneously in air. Reacts with water to generate flammable gaseous hydrogen and heat.

Question number: 109



Calcium carbonate reacts with hydroelectric acid to form carbon dioxide.

Which changes would slow this reaction down?

1. Decreasing the concentration of hydroelectric acid

2. Decreasing the particle size of calcium carbonate

3. Decreasing the temperature


Choice (4) Response








Correct option is D i. e. because the rate of reaction increases with concentration because when the acid is more concentrated, there are more acid particles in a given volume. This means there is a better chance of a successful collision occurring. If you increase the temperature, the rate of reaction will increase. This is because at low temperatures the particles don’t have as much energy, but when they are heated they take in energy which makes them move faster and collide more often. This means the collisions also have more energy, which makes more of the collisions successful. This is why as you increase the temperature the rate of reaction increases. And the decreasing the particle because is eventually soluble in HCl. As shown in figure.

Image of the caco3+hcl

Image of the caco3 + Hcl

Image of the caco3 + hcl

Image showing the caco3+hcl

Image Showing the caco3 + Hcl

Image showing the caco3 + hcl