Rate of reaction

Question 1

How does temperature affect the rate of reaction?

Answer 1

The higher the temperature the particles move quickly and collide more often with greater energy, so more collisions are successful.

Question 2

How does concentration affect the rate of reaction?

Answer 2

The higher the concentration, the particles are crowded closer together so they collide more often and so there are more successful collisions.

Question 3

How does surface area affect rate of reaction

Answer 3

The larger the surface area more particles are exposed and available for collisions, so there are more collisions and a faster reaction

Question 4

Things to remember when plotting reaction rates

Answer 4

• the steeper the line the faster the reaction
  -when one of the reactants are used up the line becomes horizontal
• same amount of products formed
  as reactants no matter the rate

Question 5

What is a catalyst?

Answer 5

A substance that increases the rate of chemical reactions without being used up in the process

Question 6

Properties of a catalyst?

Answer 6

• reduces amount of energy needed for a successful collision
  -makes more collisions successful
  -speeds up the reaction
  -provides surface area for molecules to attach to, which increase their chance of bumping into each other

Question 7

Different reactions for different catalysts?

Answer 7

• cracking of hydrocarbons uses broken pottery
  -manufacture of ammonia uses iron

Question 8

What happens in a closed system?

Answer 8

no reactants are added and no products are removed

Question 9

What is Le Chatelier’s principle?

Answer 9

If a system in equilibrium is subjected to a change in conditions, then the system shifts to resist the change

Question 10

Le chatelier’s principle - exothermic reaction?

Answer 10

-If a temperature is raised, the yield decreases - vice versa

Question 11

LCP - Endothermic reaction

Answer 11

-If temperature raised, yield decreases - viceversa

Question 12

LCP - Reaction involving gases

Answer 12

-increase in pressure favours the reaction that produces the least number of gas molecules - vice versa

Question 13

LCP- Concentration of one of the reactants or products changed

Answer 13

-system is no longer in equilibrium
-system adjusts until it can reach equilibrium once more
- If conc of one of the reactants is increased, position of equilibrium shifts so that more products are formed until eq is reached again

Question 14

Rate of reaction - measuring amount of reactant used?

Answer 14

• if one of the products is gas, measure mass in grams of the mixture before/after reaction
• mass of mixture will decrease
• Amount of reactant can be measured in moles
  -As the reaction takes place the reactant is used up, so amount of reactant is decreasing

Question 15

How is concentration of the reactant calculated?

Answer 15

amount(mol)/divided by the volume of the reaction mixture

Question 16

How to measure the amount of products formed?

Answer 16

• ## if one of the products is gas measure the total vol of gas produced with a gas syringe and the rime it takes for the reaction to happen

Question 17

Measuring the time it takes for a reaction mixture to become opaque or change colour?

Answer 17

-Time how long it takes for colour to change
- 1/time taken for colour change

Question 18

Crude oil?

Answer 18

• formed over millions of years from the remains of plankton
• found in porous rocks
• finite resource
• made from hydrocarbons

Question 19

The larger the hydrocarbon

Answer 19

-more viscous it is
- the higher its boiling point
- less volatile
- less easily it ignites

Question 20

Fractional distillation- crude oil

Answer 20

• crude oil is heated until it evaporates
• vapour moves up fractioning coloumn
• top of column much colder than bottom
  -shorter hydrocarbon molecules can reach the top of the fractioning column before they condense and are collected
  -longer hydrocarbons condense at higher temperatures and are collected lower down

Question 21

What happens to hydrocarbons during combustion?

Answer 21

• both hydrogen and carbon are oxidised
  -energy is released
• waste products produced and released into the air

Question 22

What is cracking?

Answer 22

Longer chain hydrocarbons can be broken down into shorter, more useful hydrocarbons.

Question 23

What happens during steam cracking?

Answer 23

• hydrocarbons are mixed with steam
• heated to 850 degrees

Question 24

What happens during catalytic cracking?

Answer 24

• hydrocarbons heated until vaporised
• vapour passed along a hot aluminium oxide catalyst
• thermal decomposition reaction takes place

Question 25

Alkanes and alkenes

Answer 25

• alkanes are more reactive than alkenes
• react with bromine water to turn from orange to colourless
• ethene + bromine to colourless solution
• ethane + bromine to orange brown solution

Question 26

What is meant by pure substance?

Answer 26

Only has one type of element or compound
- impure substances are mixtures

Question 27

What are formulations

Answer 27

• are mixtures that have been carefully designed to have specific properties
  -e.g: cleaning agents, paints, medicines, alloys

Question 28

What phases are there chromatography?

Answer 28

• stationary phase - absorbent paper
• mobile phase - solvent(water)

Question 29

Gas tests

Answer 29

Hydrogen - mixed with air burns with a squeaky pop
Chlorine - turns indicator paper to white
Oxygen - relights a glowing splint
Carbon dioxide - when bubbled through limewater it turn’s cloudy