C8 : Rates of reaction

Question 1

what is the rate of reaction formula?

Answer 1

rate = reactant used or product formed / time taken

Question 2

mass decrease method to calculate rate of reaction ? equipment needed?

Answer 2

EQUIPMENT :- cotton wool (gas can escape not liquid)
- hydrochloric acid
- balance

measure mass decrease at REGULAR TIME INTERVALS

Question 3

GAS SYRINGE method to calculate rate of reaction ? equipment needed? e.g?

Answer 3

EQUIPMENT : - gas syringe
- conical flask
- reactants

measure vol of gas given off at regular time intervals
e.g. 50cm cubed sulfuric acid + magnesium ribbon
-meausre time taken fro set vol of hydrogen to be given off

Question 4

volume of water method to calculate rate of reaction ? equipment needed? e.g?

Answer 4

EQUIPMENT : - delivery tube
- clamp
- measuring clinder
- water
- reactants

e.g. use dilute acid + mg to give off gas
- this creates bubbles in water, pushing water up cyclinder
- measure vol of water at regular time intervals

Question 5

diappearing cross method to calculate rate of reaction ? equipment needed? e.g?

Answer 5

EQUIPMENT : - conical flask
- sodium thisulfate
- solution
- paper with cross

e.g add 5cm cubed HCL to 50cm cubed sodium thisulfate
- goes cloudy - time taken for precipiate to form /cross to disappear

Question 6

disadvantage of using disappearing cross method?

Answer 6

-only one data point collected
-subjective

Question 7

factors affecting rate of reaction and how?

Answer 7

INCREASE CONC/PRESSURE:
-increasing conc/pressure, increases frequency of successful collisions, so rate increases
TEMPERATURE
- partciles gain KE , collide more frequently, rate increase
SURFACE AREA
- More SA:V , increases frequ of successful collisions, increasing rate
CATALYST
- provide alternative reaction pathway to products with lower activation energy
- frequ of successful collison increases

Question 8

what si meant by dynamic equilibrium?

3 MARKS

Answer 8

• occurs in a CLOSED SYSTEM
• molecules on right/left of equation will chaNge into eachother SIMULTANEOUSLY, at the SAME RATE
• conc of products/reactants will stay the SAME

Question 9

What is the Le Chatelier’s Principle?

Answer 9

If conditions of a system at equilibrium change , the position of equilibrium move to oppose the change

Question 10

what happens when you increase or decrease pressure according to chatalier’s principle?

Answer 10

INCREASE : favours reaction with FEWER MOLEUCLES OF GAS

DECREASE : favous reaction with MORE molecules of gas

Question 11

what happens when you increase or decrease temperatureaccording to chatalier’s principle?

Answer 11

increase : favours ENDOTHERMIC reaction
decrease : favours EXOTHERMIC reaction

Question 12

what happens when you increase or decrease concentration according to chatalier’s principle?

Answer 12

INCREASE : favours lower conc side
DECREASE : favours higher conc side

Question 13

what is the HABER process and conditions needed?

Answer 13

• provides a way to turn NITROGEN in the air , into AMMONIA

CONDITIONS: - nitrogen/hydrogen are PURIFIED
- 450C , 200 atm
- iron catalyst

Question 14

when equilibrium is reached, why does reaction stop?

Answer 14

the forward reaction occurs at same rate as backward reaction
- so quanities of products/reactants dont change