Rates Of Reaction

Question 1

Collision theory

Answer 1

States that in order for a reaction to occur, particles must collide with each other with enough energy to react.

Question 2

Activation energy

Answer 2

The minimum amount of energy required for a successful collision to occur

Question 3

The rate of reaction is dependent on…

Answer 3

Surface area, volume, catalysts, conc/pressure

Question 4

How does SA affect rate of reaction?

Answer 4

• increasing SA = faster rate
• smaller objects have larger SA
• there are more exposed particles on the surface of the solid = more frequent collisions
• more frequent collisions between particles = faster rate

Question 5

How does concentration of solid + pressure of gas affect rate of reaction?

Answer 5

• higher conc. of solid / higher pressure of gas = faster rate
• this is because there are more particles in the same volume
• increases frequency of collisions
• therefore increases number of successful collisions = faster rate of reaction

Question 6

How does temperature affect rate of reaction?

Answer 6

• higher temp. = faster rate
• high temp. = more kinetic energy
• makes particles move around faster
• higher frequency of collisions = more successful ones = faster rate

Question 7

What is the other reason about how temperature affects rate?

Answer 7

At higher temperatures, more particles will have energy greater than or equal to the activation energy, meaning more successful collisions will occur = faster rate

Question 8

Catalyst

Answer 8

A chemical substance that increases the rate of reaction by providing an alternate reaction pathway with a lower activation energy. It remains chemically unchanged at the end of the reaction.

Question 9

Describe the SA experiment

Answer 9

• marble chips of large + small size but the same mass are put into a conical flask each of dilute hydrochloric acid
• then time taken for the solution to produce 100cm3 of CO2 is measured for both the large and small marble chips
• the smaller ones took the least amt. of time as they had a larger SA:V ratio

Question 10

What are marble chips actually made of?

Answer 10

Calcium carbonate (CaCO3)

Question 11

Describe the concentration experiment

Answer 11

Same setup as the SA version, but the only difference is that the concentration of the hydrochloric acid is changed between 2mol/dm3 to 0.4mol/dm3 in increments of 0.4. The volume of acid remains the same

Question 12

Describe the temperature experiment

Answer 12

• sodium thiosulfate and hydrochloric acid are put into a flask inside a water bath with a black cross underneath
• then time taken for the solution to go cloudy is measured
• temperature of water bath varied between ice cold, room temp, warm and boiling water to see which made solution turn cloudy the quickest
• the boiling water one turned cloudy the quickest as high temperature increases rate

Question 13

Word equation for the temperature experiment

Answer 13

Sodium thiosulfate + hydrochloric acid => sodium chloride + sulfur + sulfur dioxide + water

Question 14

Describe the catalyst experiment

Answer 14

• 4 compounds (copper,copper oxide, manganese oxide and potassium iodide) were placed in hydrogen peroxide to see which one would catalyse its decomposition into water and oxygen
• manganese oxide was the catalyst as it made the solution effervesce vigorously and produce heat and steam

Question 15

What does hydrogen peroxide naturally decompose into?

Answer 15

Water and oxygen

Question 16

Balanced equation for decomposition of hydrogen peroxide

Answer 16

2H2O2 => 2H2O + 2O2

Question 17

What happened when copper oxide was put into the hydrogen peroxide?

Answer 17

Solution turned black (but this was because CuO is black), small bubbles were produced

Question 18

What happened when manganese oxide was put into the hydrogen peroxide?

Answer 18

Steam was produced, lots of heat and vigorous effervescence

Question 19

What happened when copper was put into hydrogen peroxide?

Answer 19

No change

Question 20

What happened when potassium iodide was put into hydrogen peroxide?

Answer 20

Solution turned yellow, effervescence and heat

Question 21

Rate of reaction formula

Answer 21

Change in amount of product/time or 1/time

Question 22

Rate of reaction units

Answer 22

Cm3/s

Question 23

How do you find rate of reaction at a specific moment on the graph?

Answer 23

• read off the x axis to see where that specific moment touches the curve
• then draw a tangent touching that specific part of the curve
• then find the gradient of the tangent using rise/run

Question 24

Explain why gradient is steep at start of experiment

Answer 24

At the start, there’s a high concentration of reactant particles. This means that:
- more frequent collisions between particles
- more frequent collisions = more successful collisions so faster RoR
- faster rate = steeper gradient

Question 25

Explain why gradient decreases as time goes on in an experiment

Answer 25

Later on, concentration of reactant particles starts decreasing. This means that: - there are less frequent collisions due to a decreasing concentration of reactant particles - less successful collisions occur - this results in a slower rate which is shown as an increasingly shallower gradient as time goes on

Question 26

Explain why gradient is 0 at the end of the experiment

Answer 26

At the end, the reaction has finished and all of the reactant particles are used up. This means that there are no particles for collisions to occur, so rate is 0 so gradient is also 0.

Question 27

How do catalysts enable companies to reduce costs?

Answer 27

They allow chemical reactions to occur at lower temperatures meaning that less energy is required for the reaction to take place, which saves money