Rates Of Reaction

Question 1

How and why does temperature affect rate of reaction?

Answer 1

• higher temp = faster RoR

* KE of particles is + ∴ move around more ∴ collide more freq ∴ more successful collisions per sec

Question 2

How do you test the affect of temperature on RoR?

Answer 2

• get 2x beakers and measure out 50ml sodium thiosulfate and 5ml of HCl
• keep the sodium thiosulfate in a baine Marie until a certain temp, e.g. 40°C
• once it has reached this temp, quickly add to the HCl in a beaker on top of a paper with a cross on it.
• time until you can no longer see cross as too cloudy

Question 3

How and why does concentration affect RoR?

Answer 3

• higher conce= faster RoR

* if conc +, more particles in the are to react ∴ greater freq reactions ∴ more success reactions per sec

Question 4

How do you test the affect of concentration on RoR?

Answer 4

• mix HCl w water in different ratios i.e. 20ml to 0ml, 8ml to 12ml 12ml to 8ml 4 ml to 6ml, to achieve different concs
• react the solution w 2g calcium carbonate chips in a test tube w a bung reading to a gas syringe at the top
• measure volume of CO2 formed in 30secs at the different concs

Question 5

How and why does surface area affect RoR?

Answer 5

• higher SA = faster RoR
• increases num particles that are exposed and available to react ∴ collisions more freq ∴ faster num of succ collisions per sec

Question 6

How do you test the affect of SA on RoR?

Answer 6

• take a 4cm long piece of rhubarb and weight it
• place in 30cm3 of potassium manganate
• time how long it takes the potassium manganate to go colourless
• repeat w same size + mass of rhubarb but each time cut it lengthways in half one more time, e.g. 2, 4, 8 pieces ∴ having different SAS, and see how long each of this takes to turn colourless

Question 7

How and why does pressure affect rate of reaction?

Answer 7

• high pres= faster RoR
• • pres means forcing gas particles closer together ∴ more freq collisions ∴ faster RoR
• only in gas reactions

Question 8

How and why does a catalyst affect rate of reaction?

Answer 8

• speeds it up
• provides an alternate route for reaction w lower activation energy ∴ less energy needed to start reaction
• is not used up during the reaction

Question 9

How do you test the affect of catalysts on RoR?

Answer 9

• hydrogen peroxide does not normally decompose. If you add managnese dioxide it will decompose to water and oxygen (formations of O₂ experiment)
• manganese dioxide remains unaltered (weigh before +after) ∴ catalyst

Question 10

What is activation energy?

Answer 10

Min amount of energy particles must colllide w for reaction to happen

Question 11

What does an RoR graph look like?

Answer 11

• time of reaction on x, amount of prod of y, ∴ rate of reaction is the grad
• steep at start as high number of particles reacting w high frequency
• becomes more shallow as the number of reactions has decreased, as they were used to form products ∴ lower RoR
• eventually stops when all reactants used up

Question 12

How do you calculate RoR?

Answer 12

RoR = amount o reactant used / time
RoR = amount of product made / time