Rates Of Reaction

Question 1

Explain reactants

Answer 1

A chemical reaction occurs when two or more substances (reactants) undergo a change whereby new products are created.
Reactants ——>Products
The reaction speed or rate can be measured as the ‘rate of formation of product’ or the ‘rate of disappearance of reactant’.

Question 2

Examples of everyday chemical reactions.

Answer 2

Examples of some everyday chemical reactions are listed below

Burning of petrol in an engine
fast
Milk turning sour
slow
Making wine from grapes
slower

Question 3

What must happen before a chemical reaction?

Answer 3

Before a chemical reaction can happen, the molecules involved must collide and have enough energy to cause a reaction. The minimum energy required for a reaction to occur between molecules is called the activation energy.

Question 4

How can you increase the rate of a chemical reaction ?

Answer 4

You can increase the rate of a chemical reaction by:
 increasing the number of collisions, or
 reducing the energy needed for the reaction to take place

Question 5

ways of making the reaction surface area of a reactant larger.

Answer 5

The following methods are all ways of making the reaction surface area of a reactant larger. They also decrease the size of the reactant particles.
 Dissolving a material in water
 grinding the material into a fine powder
 cutting the material into small pieces
 spreading the material as a fine jet

Question 6

What will happen when the effective reaction surface area is increased

Answer 6

The reaction rate will increase when the effective reaction surface area is increased (particle size is small).
A marble chip reacts fast in acid when it is crushed into a powder. A similar marble chip will react slowly if it is left as a solid lump.
Increasing the surface area of a reactant will increase the rate of a reaction.

Question 7

How can temperature effect the rate of reaction

Answer 7

When a substance is heated its molecules have more energy and move faster.
The molecules of one reactant can collide more often with those of another reactant when the temperature is increased.
Increasing the temperature of reactants will increase the rate of reaction.
For example, iron filings will react faster in hot acid compared to cold acid.

Question 8

How can concentration effect the rate of reaction

Answer 8

The greater the concentration, the more reactant molecules will be present per unit volume of the material.
There will be a greater chance for collisions to take place between reactant molecules so the reaction rate will increase.
If a gas is compressed into a smaller volume its pressure will increase and this will have the effect of increasing the concentration of the reactant gas molecules. Therefore, increasing pressure will increase the reaction rate.
A lump of marble chip will react faster in concentrated acid compared with dilute acid.
Increasing the concentration of reactants will increase the rate of reaction.

Question 9

How a catalyst can effect the rate of reaction

Answer 9

A catalyst is a chemical which makes a reaction go faster but remains unchanged after the reaction. Catalysts are very useful substances in everyday life.
Manganese dioxide added to hydrogen peroxide will cause the peroxide to decompose to water and oxygen. The manganese dioxide is the catalyst in this reaction.
A catalyst takes part in a chemical reaction, but does not get used up and can be reused with more reactants. It is chemically the same at the end of the reaction.

Question 10

Examples of every day catalysts

Answer 10

Nickel
Making margarine from vegetable oils
Vanadium pentoxide
Manufacture of sulphuric acid
Enzymes
Various chemical changes in our bodies
Iron
Manufacture of ammonia
Platinum
Manufacture of nitric acid
        Catalysts in Cars
Transition metals, for example platinum, are used as the catalysts in catalytic converters in a car exhaust.
They speed up the reaction which converts harmful gases such as nitrogen oxides and carbon monoxides into less harmful gases like nitrogen and carbon dioxide

Question 11

How can changing the variables in an experiment effect it

Answer 11

In any experiment investigating the effects of changing one variable, for example the concentration of reactants, all other variables in the investigation must be kept the same, for example temperature or the volume of reactants.
If you change two variables at the same time, you will not know which on

Question 12

Explain the reaction rate graph

Answer 12

The rate of a chemical reaction may be measured by plotting a graph of the mass of a product produced with time.