Reaction rates

Question 1

Exothermic

Answer 1

releases energy, less activation energy, change of enthalpy is negative

Question 2

Endothermic

Answer 2

absorbs energy, greater activation energy, positive change in enthalpy

Question 3

Enthalpy

Answer 3

Stored energy of a chemical substance

Question 4

Collision theory

Answer 4

For a successful collision, Particles must collide with sufficient energy to disrupt bonds of reactant particles (enough energy to get above activation energy barrier), Particles must collide with a correct orientation that is suitable for the breaking of some bonds and formation of others

Question 5

Greater the rate of successful collisions =

Answer 5

Greater reaction rate

Question 6

Activation energy

Answer 6

Minimum energy required for a collision to result, Large activation energy- slow, Small activation energy- fast rate of reaction

Question 7

Activated complex/transition state

Answer 7

unstable state which exists as bonds are broken and formed before reaction moves to completion

Question 8

Rate of reaction

Answer 8

Speed at which a chemical reaction proceeds

Question 9

How to measure reaction rate

Answer 9

Disappearance of reactants/ rate of formation of products such as Mass of substance, Volume of gas, Pressure of gas, Concentration of a substance

Question 10

Factors that control rate of reaction (6)

Answer 10

Concentration, temperature, surface area of reactants, pressure/volume, presence of a catalyst, nature of reactants (molecules or ions, ions don’t have bonds to break)

Question 11

How does concentration affect reaction rate

Answer 11

Increased concentration means there are more particles likely to collide with each other, Increased frequency of collisions but same % of successful collisions (doesn’t change), Decreased concentration means a slower rate of reaction

Question 12

How does temperature affect rate of reaction

Answer 12

Increased temp= increased average kinetic energy meaning particles have more energy, Increased energy= particles are moving faster meaning collisions are more frequent (increased frequency of collisions), % of successful collisions increases as the particles have more particles have sufficient activation energy meaning more collisions are successful- more particles can go past the activation energy barrier

Question 13

How does surface area affect reaction rate

Answer 13

Particles divided into smaller pieces means more particles are exposed meaning more reactions can take place, Increased frequency of collisions but same % of successful collisions (doesn’t change)

Question 14

How does pressure affect reaction rate

Answer 14

Only affects reactions with gasses, Increases frequency of collisions, % of successful collisions stays the same
Increased pressure= particles are closer together meaning more successful collisions take place

Question 15

What do catalysts do

Answer 15

Provide an alternative pathway with lower activation energy

Question 16

How do catalysts affect reaction rate

Answer 16

Reaction rate is increased as there is a greater % of successful collisions, More particles will have minimum energy required for a successful collision