Chapter 6 - Rates Of Reaction

Question 1

What are reactions and rates of reactions?

Answer 1

Reactions take place when particles collide with enough force to break the existing bond to allow new bonds to form. A rate of reaction therefore is the amount of succesful collisions per second
Factors affecting rate of reaction: -Temp
-pressure
- S.A
- Catalysts

Question 2

Temperature:
As particles gain energy they move faster therefore they are more likely to collide and collide with more force meaning more successful collisions per second

Answer 2

Pressure/Conc:
Increasing pressure/conc means particles are closer together therefore they are more likely to collide meaning more successful collisions per second

Question 3

S.A:
The smaller the pieces of solid in a reaction the larger the overall S.A. Inc S.A means particles have a larger area to collide with meaning they are more likely to collide therefore more successful collisions per second

Answer 3

Catalysts:
Catalyst = a substance which inc rate of a reaction without being used up itself.
It speeds up a reaction by providing an alternative route with lower activation energy so collisions require less force to take place meaning more energy can be given to more particles to collide with sufficient force. This means more succesful collisions per second

Question 4

Measuring rate of reaction

Mg + HCl > salt + X

Apparatus: Mg ribbon, 50cm³ HCl 1m, Gas syringe, stand and clamp, conical flask, stopwatch and eye protection

Answer 4

Method:

1) Measure 50cm³ HCl and pour into conical flask
2) Get stopwatch ready and check G. syringe
3) Drop Mg into conical flask and immediately place bung on top
4) measure volume of gas every 10 secs

Rate should decrease over time as more Mg is used up

Question 5

Rate of Reaction + concentration

Apparatus: 40cm³ 2m HCl, 200cm³ sodium thiosulphate solution, 100cm³ 
Measuring cylinder (for Sodium T), 100cm³  measuring cylinder (for water), 10/25cm³ measuring cylinder (for acid), conical flask, stopwatch and eye protection

Answer 5

Method:
1) Put on eye protection
2) mix sodium thiosulphate and water in a conical flask using volumes shown below.
3) Add acid to flask, swirl content and start S.W
4) place flask on pencilled mark on white paper
5) Record time when cross disappears
Volumes: Sth- 50 40 30 20 10
H2O 00 10 20 30 40
HCl 05 05 05 05 05
More concentrated = quicker

Question 6

Effect of surface area on rates of reaction

Answer 6

Method:
1) Add 5g of large marble chips to a conical flask
2) To it add 30cm³ of HCl and place bung on and start stop watch
3) Read volumes produces every 10 secs from Gas syringe
4) Plot a graph against time(s)
5 Repeat with 5g of smaller chips

Smaller chips have faster rate of reaction