Topic 6 - Rates of Reaction

Question 1

what is the mean rate of reaction?

Answer 1

reactant used OR product formed / time

Question 2

what are the 3 ways of measuring rate of reaction?

Answer 2

• precipitation
• change in mass
• volume of gas given off

Question 3

advantages of precipitation

Answer 3

• simple
• easy to carry out

Question 4

disadvantages of precipitation

Answer 4

• only works for reactions where there’s a visual change
• results are subjective as people may disagree when the mark ‘disappears’
• can’t plot rate of reaction graph

Question 5

advantages of change in mass

Answer 5

• most accurate as the mass balance very accurate
• easy to carry out
• can plot a rate of reaction graph

Question 6

disadvantages of change in mass

Answer 6

• releases the gas straight into the room
• if gas is harmful, carry out the reaction in a fume cupboard

Question 7

advantages of volume of gas

Answer 7

• can plot a rate of reaction graph
• gas syringes give volumes to nearest cm3 : very sensitive
• gas isn’t released into the room

Question 8

disadvantages of volume of gas

Answer 8

• if the reaction is too vigorous you can blow the plunger out the end of syringe
• quite hard to set up: lot of equipment

Question 9

what do reaction graphs with a fast rate of reaction look like

Answer 9

• it has the steepest curve at the beginning
• shows products are being formed more quickly
• takes a shorter time to level off
  ( plateau )

Question 10

what do reactions with more reactants look like

Answer 10

• they plateau off at a higher level as a higher amount of products are being formed

Question 11

why does the rate of reaction decrease over time?

Answer 11

• the rate of a reaction is directly proportional to the concentration of reactants.
• As the reaction proceeds, the reactants are converted into products,
• which causes the concentration of reactants to decrease
• and the rate of the reaction to slow down

Question 12

factors that affect the rate of reaction:

Answer 12

• temperature
• concentration
• surface area

Question 13

collision theory
( 2 things )

Answer 13

• for particles to react they have to collide with each other with sufficient energy
• this is called the activation energy
• the more frequent the collisions are, the faster the rate of reaction

Question 14

temperature ( frequency of reactions )

Answer 14

• when temp increased, particles move quicker
• this means they will collide more frequently which means faster rate of reaction

Question 15

temperature ( activation energy )

Answer 15

• increasing temp also increases amount of energy particles have
• more particles will have activation energy required
• more successful reactions

Question 16

concentration

Answer 16

• more concentrated means the particles of the reactant are more densely packed together
• leads to more frequent collisions between the relevant particles
• rate of reaction will increase

Question 17

surface area

Answer 17

• a greater surface area means the particles around it in solution will have more area to work on
• this leads to more frequent collisions
• rate of reaction will increase

Question 18

how to increase SA : V ratio of substances

Answer 18

• if it is a solid, crushing it into a powder increases SA : V ratio

Question 19

rate and proportionality

Answer 19

the rate of the reaction is directly proportional to the frequency of successful collisions

Question 20

what are catalysts?

Answer 20

a substance which can speed up the rate of reaction without being used up or changing the reaction products

Question 21

how do catalysts speed up the rate of reaction?

Answer 21

• it provides an alternative reaction pathway with a lower activation energy
• more particles have the required activation energy leading to more successful collisions

Question 22

what are enzymes?

Answer 22

• BIOLOGICAL catalysts that speed up rate of reactions in living organisms

Question 23

what are yeast cells used for?

Answer 23

• zymases are enzymes from yeast cells
• catalyse the reaction that converts sugars into ethanol and carbon dioxide
• fermentation