Rates of reaction

Question 1

Define exothermic reactions.

Answer 1

transfers energy to surroundings, so temp rises

Question 2

Define endothermic reactions.

Answer 2

Takes in energy from surroundings, so temp falls.

Question 3

What is the activation energy?

Answer 3

The minimum amount of energy needed required for particles to collide and react.

Question 4

Where is activation energy found on exo/endo graphs?

Answer 4

Line from curve to reactants.

Question 5

In exo graphs, are reactants higher or lower energy than products?

Answer 5

Higher

Question 6

In endo graphs, are reactants higher or lower energy than products?

Answer 6

Lower

Question 7

Explain the differences between endo and exo graphs.

Answer 7

Reactants>products, exo
Product>reactants, endo
In exo, energy is released rather than absorbed (reactants to products)

Question 8

RQ4: Give the method of finding temperature changes.

Answer 8

-measure 30cm3 of HCl acid into polystyrene cup and measure temp.
-measure 5cm3 of NaOH into polystyrene cup.
-place lid with thermometer
-repeat 3 times and increase by 5cm3 each time

Question 9

What is bond energy?

Answer 9

Amount of energy required to break one mole of a particular covalent bond

Question 10

How do we know if a reaction is endothermic or exothermic using bond energies?

Answer 10

Reactant>product(+), Endo
Products>reactants(-), Exo

Question 11

What is meant by ‘rate of reaction’?

Answer 11

Speed at which reactants turn into products

Question 12

What are the 2 formulas to find the average rate of reaction?

Answer 12

Amount of reactants used up/time taken
Amount of products formed/ time taken

Question 13

Why is a mean calculated for rates of reaction?

Answer 13

In reality, product formed is fast then slows down

Question 14

Explain the collision theory.

Answer 14

For particles to react, they need to have sufficient energy and correct orientation to achieve activation energy

Question 15

What are the 2 things that can increase a rate of reaction?

Answer 15

1- Amount of energy
2- Frequency of collisions

Question 16

What are the factors that cause either an increase in energy or frequency of collisions?

and explain them

Answer 16

-Temperature, more energy = more collisions
-Pressure, more likely to collide
-Surface area of reactant, powder has more area over which collisions occur
-Catalyst, speeds up reaction by lowering activation energy

Question 17

RP5: Effect of concentration on rate of reaction in liquids

Answer 17

Measure 50cm3 of sodium thiosulfate solution, measure 5cm3 HCl into a measuring cylinder, add to flask on top of paper with a cross, add acid into flask + start the stopwatch, stop when cross not seen, repeat using different concentrations of sodium thiosulfate solution.

Question 18

What causes the reaction of sodium thiosulfate and HCl to become cloudy

Answer 18

Sulfur as product

Question 19

RP5: Effect of concentration on rate of reaction in gases

Answer 19

Measure 50 cm3 dilute HCl into a flask, add Mg ribbon into flask and connect it to the gas collection equipment (syringe), start stopwatch and record the volume of gas every 10 seconds, When reaction completes, repeat using higher conc of HCl

Question 20

What is the problem with using crosses and cloudiness of reaction to measure rate of reaction?

Answer 20

Eyesight, people may have different levels

Question 21

For particles to react successfully, they must…

Answer 21

1- collide
2- reach activation energy
3- collide in correct orientation

Question 22

What is meant by a reversible reaction?

Answer 22

Reactants can form products, and products can form reactants

Question 23

If a reversible reaction is exothermic in one direction, it is..

Answer 23

endothermic in the other direction

Question 24

Explain how equilibrium is achieved.

Answer 24

When a reaction is being carried out, the forward reaction will be faster than the backwards (since there are more reactants than products), then the backwards reaction speeds up and the rate will equal eachother

Question 25

Define equilibrium

Answer 25

When the rate of forwards and backwards reactions are equal (doesn’t mean amount of reactants and products are equal)

Question 26

If equilibrium is to the right, what does it mean?

Answer 26

When the reaction is at equilibrium but there are more products

Question 27

What is Le Chatelier’s principal?

Answer 27

If a change is made to an equilibrium in a reversible reaction, it will shift to oppose this change.

Question 28

If we increase the temperature of the reactants, the equilibrium will shift to…

Answer 28

The left to form more reactants

Question 29

If we increase the concentration, the equilibrium will shift to the…

Answer 29

the side with less molecules (concentration) so the right