Kinetics

Question 1

What must happen for a reaction to take place?

Answer 1

Particles must collide with enough energy to break the bonds holding them together in order to start the reaction.

Question 2

The more successful collisions:

Answer 2

The faster the rate of reaction.

Question 3

What is Activation Energy?

Answer 3

The minimum amount of energy the particles must collide with in order to start the reaction.

Question 4

Particles must also have …

Answer 4

The correct orientation to react. (Specifically shaped active sites)

Question 5

How does increasing the temperature increase the rate of reaction?

Answer 5

• Energy Transferred to kinetic stores = move faster, more chance of colission. They have more energy and are more likely to have the activation energy.

Question 6

How does increasing the concentration or pressure of a gas increase the rate of reaction?

Answer 6

More particles in the same volume/are meaning there is an increased chance of colission.

Question 7

How does a catalyst increase the rate of reaction?

Answer 7

Provides an alternative reaction pathaway with a lower activation energy.

Question 8

How does increasing the surface area of a solid increase the rate of reaction?

Answer 8

The greater the surface area of a solid, the more of its particles are able to react with molecules in a gas or a liquid. Breaking it up means there are more sites for reaction.

Question 9

Breaking bonds is…

Answer 9

Endothermic because the amount of energy needed to break the bonds is greater than the amount of energy released by forming them.
(Requires energy)

Question 10

Creating bonds is…

Answer 10

Exothermic because the energy released by creating bonds is greater than the energy used to form them.
(Releases energy)

Question 11

What happens if you plot a graph of energy against the fraction of particles with that energy?

Answer 11

You get a curve in a shape called the Maxwell-Boltzmann Distribution.

Question 12

What does the Maxwell Botzmann Distribution tell us? (4)

Answer 12

• no particles have 0 energy.
• most particles have intermediate energy.
• a few have very high energies.
• the average energy is not the same as the most probable energy.

Question 13

The need for the activation energy to be present before any reaction shows…

Answer 13

Explains why not all reactions that are exothermic occur spontaneously at room temperature.

Question 14

How does the shape of the Maxwell Boltzmann Distribution graph change with temperature?

Answer 14

The peak of the curve is lower and moves to the right and the particles with high energy increases.
This shows that at a higher temperature, more particles have energy greater than the activation energy which is why more collisions happen.

Question 15

A small increase in temperature causes…

Answer 15

A large increase in the number of particles with energy greater than the activation energy.

Question 16

Particles must also collide in…

Answer 16

the right direction.

Question 17

What is the Rate?

Answer 17

The change in amount or concentration of a product or a reactant per unit time.

Question 18

What are Catalysts?

Answer 18

Substances that speed up the rate of a chemical reaction without being changed or used up - they lower the activation energy.

Question 19

What is a catalytic converter?

Answer 19

A honeycomb ceramic material coated with platinum and rhodium metals (catalysts) and as polluting gases pass over them they rest with eachother and form less harmful products.

Question 20

What reactions take place because of the catalytic converter?

Answer 20

Carbon monoxide + nitrogen oxides ——> nitrogen and carbon dioxide.

Hydrocarbons + nitrogen oxides ——> nitrogen and carbon dioxide and water.

Question 21

How do the catalytic converter reactions take place?

Answer 21

• gases form weak bonds with the metal atoms (adsorption) holds the gases in right place , they react.
• products break away from metal atoms (desorption) frees up room on the catalyst surface for more gases to take their place and react.

Question 22

What are zeolites?

Answer 22

Minerals that have a very open structure that ions and molecules can fit into - confine molecules into small spaces. Used as catalysts.

Question 23

What is done to hardening fats?

Answer 23

Unsaturated fats are made more solid when hydrogen is bubbles into the liquid fat which has a nickel catalyst mixed with it.

Question 24

How can you measure reaction rates? (3)

Answer 24

• how long a precipitate takes to form (using the cross)
• measuring a decrease in mass (how quick the mass decreases when a gas is released)
• measuring the volume of gas given off (using a gas syringe)

Question 25

What do sodium thiosulfate and hydrochloric acid react to form?

Answer 25

A yellow precipitate of sulfur.

Question 26

Give the steps to the sodium thiosulfate and hydrochloric acid practical for rate of reaction:

Answer 26

• measure fixed volume of each
• use water bath to heat them to the desired temperature before you mix them.
• put them in a conical flask and put the flask over a black cross - see how long it takes for it to disappear.

Question 27

What can you do with the sodium thiosulfate and hydrochloric acid practical?

Answer 27

Repeat at different temperatures - make sure the concentration and depth of liquid is kept the same though.