Reaction Rates

Question 1

A + B →

Answer 1

C + D

Question 2

Define reaction rate

Answer 2

number of moles of product formed per second.
or
number of moles of reactant used per second

Question 3

What is the unit for reaction rate

Answer 3

mol / s

Question 4

What are the 4 methods for reaction rates

Answer 4

1) mass change
2) volume of gas
3) solid disappearing
4) color change

Question 5

What is the reaction rate represented by on a graph?

Answer 5

the gradient

Question 6

Define tangent

Answer 6

straight line that has the same gradient as 1 point on a curve

Question 7

What is one way mass change can be measured?

What would you measure?

Answer 7

by measuring the volume of gas made / used up

Question 8

Why does the mass decrease when measuring mass change in a reaction between metal carbonate and acid?

Answer 8

because gas is produced, and as it goes out of the top of the conical flask and therefore the mass left in the flask is less than what is started at

Question 9

Why shouldn’t you measure the initial volume of gas produced when measuring volume of gas?

Answer 9

because no gas is produced initially

Question 10

What does a graph of measuring the mass change in a reaction with a metal carbonate and an acid look like?

Answer 10

add photo at home

Question 11

What does a graph of measuring the volume of gas in a reaction with a metal and an acid look like?

and tangent

Answer 11

add photo at home

and tangent

Question 12

What would you measure in a reaction of solid disappearing?

Answer 12

time until solid disappears

Question 13

What are the problems with using solid disappearing as a rate of reaction?

Answer 13

• can only calculate average rate
• no graph

Question 14

What would you measure in a reaction of color change?

Answer 14

time until color change is observed

Question 15

What are the problems with using color change as a rate of reaction?

Answer 15

• no graph
• can only calculate average rate
• subjective

Question 16

Give an example of a color change reaction

Answer 16

iron (gray) + copper sulfate (blue) → iron (II) sulfate (green) + copper (orange)

Question 17

What apparatus is needed when measuring volume of gas?

Answer 17

• gas syringe

Question 18

Describe the ‘flow’ of a rate of reaction from beginning to end

Answer 18

the rate always decreases from beginning to end

Question 19

Why does the rate of reaction decrease?

Answer 19

because the rate of collisions decreases

Question 20

What happens when when reactants are used up during a reaction?

Answer 20

fewer particles are available

Question 21

What happens at the end of a reaction?

Answer 21

there are no more reactants available therefore no collisions can occur

Question 22

What do particles have to do in order for a reaction to happen?

Answer 22

they have to collide

Question 23

What 2 properties are needed for particles to be able to collide?

Answer 23

1) sufficient energy
2) correct orientation

Question 24

What is energy used for in a reaction?

Answer 24

to break the bonds of the reactants

Question 25

Are most collisions successful or unsuccessful?

Answer 25

unsuccesful

Question 26

What can be done to increase rate of reaction?

Answer 26

1) increase frequency of collisions
2) increase the proportion of successful collisions

Question 27

What can be done to increase the proportion of successful collisions?

Answer 27

1) change energy of particles
2) change orientation of particles

Question 28

What 4 factors affect rate of reaction?

Answer 28

1) temperature
2) surface area
3) catalysts
4) concentration / pressure

Question 29

Write a general method for measuring the effect of surface area of a rate of reaction

Answer 29

1) measure x cm³ (25 cm³) of HCL into a conical flask using a measuring cylinder
2) record mass of apparatus
3) record mass of CaCO₃
4) add CaCO₃ to HCl on a balance
5) start timing
6) record mass every 20 seconds until the reaction ceases
7) repeat with equal mass of CaCO₃ powder

Question 30

What will increasing the temperature do to a rate of reaction?

Answer 30

increase the rate of reaction

Question 31

What 2 factors make increasing the temperature increase the rate of a reaction?

Answer 31

1) particles gain kinetic energy, move faster and collide more frequently (this effect is minor, there is only a slight change in collision frequency)

2) proportion of particles with Ea is increased

Question 32

Does an energy profile indicate rate of reaction?

Answer 32

no

Question 33

Does the energy change depend on the rate of reaction?

Answer 33

no, the energy change will be the same regardless if the reaction occurs faster or slower

Question 34

Define Ea

Answer 34

the minimum energy required for particles to react (energy needed to break bonds in reactants)

Question 35

What are the axis in a Maxwell - Boltzmann distribution graph?

Answer 35

X - axis - energy
Y - axis - frequency / number of particles

Question 36

Explain and Describe the Maxwell - Boltzmann distribution

Answer 36

on the black curve, the part shaded in pink are the particles with enough energy (Ea or 50 kJ / mol) that can collide, with the temperature at 25 ºC. the pink line shows the temperature that was then increased to 50 ºC. now the region in bronze shows that there are more particles with the minimum Ea (50 kJ / mol) available to react. this increases the frequency of successful collisions. this significantly increases the rate of the reaction

Question 37

Define temperature

Answer 37

the average energy / movement of particles in a sample

Question 38

Why are most collisions unsuccessful?

Answer 38

because one or both particles have insufficient energy (Ea)

Question 39

Define catalyst

Answer 39

a substance that increases the rate of a reaction without being used up in a reaction

Question 40

How can catalysts affect the rate of a reaction?

Answer 40

1) affect the frequency of collisions
2) increase the proportion of collisions with the correct orientation
3) increase proportion of particles with Ea

Question 41

Most catalysts are heterogenous to the reactants. What does this mean?

Answer 41

catalysts are a different state to the reactants

Question 42

Is a rate of reaction without a catalyst fast or slow?

Answer 42

slow