Rates of reaction

Question 1

How do you find the rate of reaction?

Answer 1

reactant used/ time
product made/ time

measured in g/s, cm^3/s, mol/s

Question 2

How can you measure an observable change?

Answer 2

• loss in mass of reactants
• measure volume of gas produced
• time for solution to become opaque

Question 3

How do you measure how much mass is lost in a reaction?

Answer 3

• carry reaction out on balance
• used if gas is produced

Question 4

How do you measure the volume of gas produced in a reaction?

Answer 4

• use gas syringe
• used if gas is produced

Question 5

What is the disappearing cross investigation?

Answer 5

• used if solid is formed
• mixture becomes cloudy as solid is produced in reaction
• time how long it takes for cross to disappear
• longer the time, slower the reaction

Question 6

How do you calculate the rate of a reaction between two times from a graph?

Answer 6

• draw lines up from x axis to y axis
• quantity of produce formed/ time taken

Question 7

How do you calculate the rate of reaction for a single given time?

Answer 7

• draw tangent at point
• calculate gradient (change in y/ change in x)

Question 8

What factors can affect the rates of chemical reactions?

Answer 8

• concentration
• gas pressure
• surface area
• temperature
• catalyst

Question 9

How does concentration increase the rate of chemical reactions?

Answer 9

• increase concentration = increases number of particles in same volume
• increases frequency of collisons

Question 10

How does gas pressure increase the rate of reaction?

Answer 10

• increases number of gas molecules in same volume
• increases frequency of collisions

Question 11

How does surface area increase the rate of reaction?

Answer 11

• smaller pieces = greater surface area
• increases frequency of collisions

Question 12

How does increasing temperature increase the rate of reaction?

Answer 12

• particles gain more energy/ move faster
• increases frequency of collisions
• more successful collisions, more have energy greater than activation energy

Question 13

How does using a catalyst increaese the rate of reaction?

Answer 13

• not used up
• provides different pathway for reaction, lower activation energy
• different reactions need different catalysts
• enzymes act as catalysts in biological systems

Question 14

Describe an investigation to find how concentration affects the rates of reacitons by measuring the volume of gas produced

Answer 14

1) weigh 5g of marble chips on balance
2) put marble chips into flask
3) measure 25cm^3 of hydrochloric acid using measuring cylinder
4) pour acid into flask, connect gas syringe and start timer
5) repeat using different conc. of acid

Question 15

Describe an investigation to find how concentration affects the rates of reactions by looking at the change in colour or tubidity)

Answer 15

1) measure 25cm^3 of sodium thiosulfate using measuring cylinder
2) place into conical flask
3) stand flask on paper with cross on
4) meausre 5cm^3 of hydrochloric acid using measuring cylinder
5) pour acid into flask, start timer
6) record time taken until cross is obscured from view
7) repeat using differnet conc. of sodium thiosulfate

Question 16

How do you investigate the effect of changing temperature on rate of reactions?

Answer 16

• heat reactants to required temp. using water bath