6.2 rate of reaction

Question 1

Rate of reaction defination

Answer 1

The rate of reaction is a measure of how fast or slow a chemical reaction is

Question 2

how is rate of reaction calculated

Answer 2

It is calculated by how much reactant is used per unit time OR how much product is produced per unit time

Question 3

factors that effect the rate of reaction

5 factors

Answer 3

• concentration of solutions
• pressure of gases
• surface area of solids
• temperature
• catalyst

Question 4

Increasing the concentration of a solution increases the collision rate

Answer 4

there will be more reactant particles per unit volume, causing more frequent collisions so there are more successful collisions per second, increasing the rate of reaction

Question 5

Increasing the surface area of a solid increases the collision rate

Answer 5

more of the solid particles will be exposed to the other reactant so there will be more frequent collisions and therefore more successful collisions per second, increasing the rate of reaction

Question 6

Increasing the temperature increases the rate of reaction

Answer 6

As temperature increases the particles gain kinetic energy, and so move around more quickly. This means that they collide more frequently and with more energy. Therefore, there will be more collisions that surpass the activation energy, so the rate of reaction will increase

Question 7

what is a catalyst

Answer 7

a catalyst increases the rate of a reaction and is unchanged at the end of a reaction

Question 8

When a catalyst is used, the rate of reaction will increase

Answer 8

• Catalysts (including enzymes) create alternative reaction pathways which have a lower activation energy
• This means that more collisions will have sufficient energy to be successful

Question 9

explain the factor Temperature using collion theory

Answer 9

• At low temperatures only a small number of particles will have the required activation energy so the reaction will be slow
• At higher temperatures the particles have more kinetic energy so they move faster and with more energy
• The collisions are therefore more energetic, and there are then a greater number of particles with sufficient energy to react, so the rate of reaction increases

Question 10

Activation energy

Answer 10

minimum amount of energy required for a reaction to take place

Question 11

explain factor Concentration
using collision thoery

Answer 11

• Increasing the concentration means there are more particles per cm3, so there is less space between the particles
• Since there are more particles then it follows that there are more frequent collisions, increasing colllision rate and so the rate of the reaction increases

When answering questions on the effect of concentration on the rate of reaction, you should mention that there are more particles per unit volume (usually cm3) and this causes an increase in the rate of collisions.

Question 12

explain Graph showing the effect of the concentration of a solution on the rate of reaction

Answer 12

• Compared to a reaction with a reactant at a low concentration, the graph line for the same reaction but at a higher concentration has a steeper gradient at the start and becomes horizontal sooner
• This shows that with increased concentration of a solution, the rate of reaction will increase
• As long as the reactant having its concentration changed is already in excess, the amount of product formed will not change, but will simply be formed faster

Question 13

explain graph showing the effect of the surface area of a solid on the rate of reaction

Answer 13

• Compared to a reaction with lumps of reactant, the graph line for the same reaction but with powdered reactant has a steeper gradient at the start and becomes horizontal sooner
• This shows that with increased surface area of the solid, the rate of reaction will increase

Question 14

graph showing the effect of catalyst on the rate of reaction

Answer 14

• Compared to a reaction without a catalyst, the graph line for the same reaction but with a catalyst has a steeper gradient at the start and becomes horizontal sooner
• This shows that when a catalyst is used, the rate of reaction will increase
• A catalyst will never change how much product is made

Question 15

explain Graph showing the effect of temperature on the rate of reaction

Answer 15

Explanation:

• Compared to a reaction at a low temperature, the graph line for the same reaction but at a higher temperature has a steeper gradient at the start and becomes horizontal sooner
• This shows that with increased temperature, the rate of reaction will increase
• Temperature will not affect how much product is made in an irreversible reaction

Question 16

Explaining the shape of the graph

Answer 16

• The steeper the curve, the faster the rate of the reaction
• The curve is steepest initially so the rate is quickest at the beginning of the reaction
• As the reaction progresses, the concentration of the reactants decreases, the rate decreases shown by the curve becoming less steep
• When one of the reactants is used up, the reaction stops, the rate becomes zero and the curve levels off to a horizontal line
• The amount of product formed in a reaction is determined by the limiting reactant:
  -If the amount of limiting reactant increases, the amount of product formed increases
  -If the amount of the reactant in excess increases, the amount of product remains the same