Rate and extent of chemical change(Unit 6)

Question 1

How do you measure rate of reaction (give units)?

Answer 1

Quantity of Reactant Used / time (s)
The quantity of Product Used / time (s)
(cm³/s OR g/s OR mol/s)

Question 2

How do you find the AVERAGE rate of a reaction (that produces gas)?

Answer 2

Measure change of mass (quantity of reactant used) over time
OR
Volume of gas produced (change in product) over time

Question 3

What two ways can you measure volume of gas produced in cm³?

Answer 3

1) Use a gas syringe. Read of cylinder
2) Put a measuring cylinder filled with water upside down in a trough filled with water (not to the brim). Connect it to a flask via a delivery tube. Measure at bottom of the meniscus

Question 4

When would you prefer to use a gas syringe over the ‘cylinder in trough’ method?

Answer 4

If the gases tested are soluble as you would not want it to dissolve in water if using cylinder method.

Question 5

What is an issue with using the gas syringe method?

Answer 5

It is prone to leaking.

Question 6

How do you find the rate of a reaction AT DIFFERENT STAGES?

Answer 6

• Record the quantity of product formed/reactants used or lost at regular timed intervals.
• Plot on a graph and find tangent, where the gradient = rate.

Question 7

When seeing a rate of reaction graph, what is usually the pattern?

Answer 7

1) Initially, there is a fast rate and steep gradient
2) The rate of reaction slows/gradient decreases
3) Line flattens out and reaction stops.

Question 8

Why does a reaction stop?

Answer 8

There are no more reactants left to react

Question 9

When comparing different rates of reaction, what things can you compare? Say how you can tell.

Answer 9

1) The rate of reaction (shown by gradient)
2) How long the reaction took (seeing where cut-off point is/how far down x-axis)
3) Amount of product formed (how far the cut-off point is up the y-axis)

Question 10

What are on the axis on rate of reaction graphs?

Answer 10

x-axis shows time

y-axis shows amount of product formed

Question 11

What factors affect the rate of a reaction?

Answer 11

1) Temperature
2) Concentration
3) Pressure
4) Surface Area of Reactants
5) Catalyst

Question 12

How does an INCREASE in temperature INCREASE the rate of reaction?

Answer 12

1) The particles are given more kinetic energy, therefore move around more and faster.
2) This results in MORE frequent and MORE successful collisions
3) This increases the rate of reaction

Question 13

How does an INCREASE in concentration INCREASE the rate of reaction?

Answer 13

1) There are more reactant particles dissolved per unit volume
2) This means there are more particles to react with
3) This results in MORE frequent and MORE successful collisions
4) This increases the rate of reaction

Question 14

What is the caveat of increasing concentration?

Answer 14

It only applies to solutions or liquids

Question 15

What is a fluid?

Answer 15

Liquid or Gas or Aqueous Solution (something you can pour)

Question 16

How does an INCREASE in pressure INCREASE the rate of reaction?

Answer 16

1) There are more (reactant) particles per unit volume of gas
2) This results in MORE frequent and MORE successful collisions
3) This increases the rate of reaction

Question 17

What is the caveat of increasing pressure?

Answer 17

It only applies to gaseous reactions.

Question 18

How does an INCREASE in surface area INCREASE the rate of reaction?

Answer 18

1) There are more particles exposed/to react with at the surface at once
2) This results in MORE frequent and MORE successful collisions
3) This increases the rate of reaction

Question 19

How does a catalyst speed up the rate of reaction?

Answer 19

(It provides a surface to react on)

1) It provides a different chemical pathway that requires a lower Activation Energy
2) It DOES NOT increase the frequency of collisions, but increases the frequency of SUCCESSFUL collisions
3) This is because particles need LESS energy to get a SUCCESSFUL collision
4) This increases the rate of reaction

Question 20

How specific are catalysts in a reaction?

Answer 20

They are specific to a reaction

Question 21

What is a catalyst?

Answer 21

• Substance that speeds up the rate of a reaction
• It does not alter the products of the reaction
• It is not chemically changed or used up at the end of the reaction

Question 22

What is an industrial advantage of using catalysts?

Answer 22

It results in less energy resources needed for reactions to occur.

Question 23

Is the temperature, concentration of solution, gas pressure, and surface area proportional to the rate of reaction?

Answer 23

Temperature- NO (only little increase in temp. needed to increase rate)
Surface Are/Concentration/Pressure- YES

Question 24

How do you identify if a catalyst has been used in a reaction when given a question?

Answer 24

If the rate of reaction has increased, and there is no catalyst included in equation.

Question 25

What is ‘Activation Energy’?

Answer 25

Minimum amount of energy needed to start a reaction

Question 26

What is ‘Collision Theory’?

Answer 26

Theory that chemical reactions occur when reacting particles collide with each other WITH SUFFICIENT ENERGY