Chemistry - Rate of Reactions

Basic flashcards of Rates of Reactions, GSCE Standard Level.

Rate of Reaction

The time taken for a reaction to go to completion.

How is the rate of reaction measured?

An increase in the amount of product/A decrease in the amount of reactants.

What changes occur in a chemical reaction?

• Colour change

• Formation of a precipitate

• Measuring the volume of gas evolved

• Time taken for the reactant/s to disappear

• Changes in pH

How can a curve be interpreted in a rate of reaction graph?

The steeper the slope, the faster the reaction.

The Collision Theory

Upon collision existing chemical bonds between atoms are broken and new bonds are formed when the atoms recombine to form a product.

Factors affecting the rate of reaction

• Concentration/pressure

• Temperature

• Light intensity

• Physical nature

• Catalysts

Why does the rate of reaction increase when the concentration increases?

Because the particles are packed more closely together and so collisions between the particles occur more frequently.

What is the balanced chemical equation for the reaction between sodium thiosulphate and hydrochloric acid? (This experiment is used to test on rate of reaction)

Na₂S₂O₃(aq) + 2HCl(aq) → S(s) + 2NaCl(aq) + SO₂(g) + H₂O(l)

Why does the rate of reaction increase when the temperature is increased?

When the temperature increase, the particles absorb kinetic energy and move faster, and so increase the possibility of colliding into each other. So, they react faster.

When the surface area is increased, what happens to the rate of reaction?

The rate of reaction increases.

When light intensity increases, why does the rate of reaction also increase? (For certain reactants only)

In the presence of light, photoreduction takes place.

Catalyst

A catalyst is a substance the alters the rate of reaction without being chemically changed.

When a catalyst is used, what happens to the activation energy (E_a)?

The activation energy (E_a) decreases.

Activation energy

The minimum amount of energy needed for a reaction to occur.

The properties of catalysts

• They are transition metals or compounds containing transition metals

• They don’t affect the equilibrium position.

• Catalysts are specific.

• They remain chemically unchanged and can be reused.

• Small amounts are enough to catalyse a reaction.