Topic 7 - rates of reaction & energy changes

Question 1

DESCRIBE CORE PRACTICAL :

different conditions for marble chips

Answer 1

• investigating the effect on rate of changing the size of the marble chips (smaller chips=larger surface area= faster rate)
• and the effect of changing the concentration of HCl

Question 2

effect of temperature on rate of reaction

Answer 2

• rate of reaction will increase, because the heat gives the particles more kinetic energy
• there will be more collisions per second and collisions will have more energy, so there’s more successful collisions, since they have the energy to complete reactions

Question 3

effect of concentration on the rate of reaction

Answer 3

• no. of acid particles are increased (in the given volume)

- so the number of collisions per second between the reactants are increased, so rate of reaction increases

Question 4

effect of increased surface area on rate of reaction

Answer 4

• there’s more exposed surface for the reacting particles to collide with, so there’s more collisions per second

Question 5

rate of reaction equation

Answer 5

= amount of reactant used/ Time or

= amount of product formed/ time

Question 6

how would you measure the amount of product formed (rate of reaction)

Answer 6

• if product is a gas, measure the volume of gas produced in a gas syringe

Question 7

how would you measure how much reactant is used

Answer 7

• if product is a gas, which will be given off, carry out the reaction on a set of weighing scales and measure
  how much mass is lost

Question 8

how would you measure how much reactant is used

rate of reaction

Answer 8

• if product is a gas, which will be given off, carry out the reaction on a set of weighing scales and measure
  how much mass is lost

Question 9

Describe ‘activation energy’

Answer 9

• the minimum amount of energy required for chemical reactions to occur
• so the reacting particles will collide with enough energy,

Question 10

how does increasing the rate of reaction affect the activation energy

Answer 10

• to increase the rate of a reaction, you need to increase the frequency/energy of collisions, so that more of them reach the activation energy

Question 11

methods to increase the rate of reaction

Answer 11

• increasing temp., pressure, concentration, surface area or by using a catalyst

Question 12

How does increasing pressure affect the rate of reaction

Answer 12

• molecules have less space in which they can move. That greater density of molecules increases the number of collisions
• it increases the number of particles in a given volume so increases the frequency of collisions

Question 13

how to find the rate of reaction graphically

Answer 13

• Draw tangents to curves and use the slope of the tangent as a measure of the rate of reaction

Question 14

What is a catalyst

Answer 14

• substances that speed up chemical reactions without being changed or used up during the reaction.
• They have the same mass at the end of the reaction

Question 15

how does a catalyst affect the activation energy

Answer 15

• they decrease the activation energy
• this increases the amount of particles w/ energy to
  react, so there are more frequent successful collision so an increased rate of reaction
  ● & they lower the activation energy by providing a different pathway for a chemical reaction that has a lower activation energy

Question 16

example of a catalyst used in real life

Answer 16

Enzymes act as catalysts in biological systems

Yeast is the enzyme used in the production of ethanol & ethanol is used in alcohol

Question 17

is a neutralisation reaction exo or endothermic

Answer 17

• exothermic

Question 18

examples of reactions that can be exo or endothermic

Answer 18

• salts dissolving in water

- displacement reactions

Question 19

is precipitation an exo or endothermic reaction

Answer 19

• exothermic

Question 20

how to measure an exo/endothermic reaction

Answer 20

• if reactions take place in a solution, you can carry them out in a polystyrene cup with a lid, and measure the temperature change using a thermometer

Question 21

What is an exothermic reaction and examples

Answer 21

• one that transfers energy to the surroundings so the
  temperature of the surroundings increases.
  e.g. combustion, many oxidation reactions and neutralisation.
  ● Everyday examples are self-heating cans (e.g for coffee) and hand warmers

Question 22

What is an endothermic reaction and examples

Answer 22

• it takes in energy from the surroundings so the temp. of the surroundings decreases.
  e.g. thermal decomposition and the reaction of citric acid and sodium hydrogencarbonate.
  ● Some sports injury packs are based on endothermic
  reactions

Question 23

is breaking bonds an exo/endothermic reaction

Answer 23

• endothermic

Question 24

is making bonds exo/endothermic reaction

Answer 24

• exothermic

Question 25

Why is bond breaking an endothermic reaction

Answer 25

• Energy must be SUPPLIED to BREAK bonds in the reactants

Question 26

Why is bond making an exothermic reaction

Answer 26

• Energy is RELEASED when bonds in the products are FORMED

Question 27

How to calculate energy change (equation)

Answer 27

Sum of energy taken in to break bonds – sum of energy released to form bonds = overall energy change

Question 28

What is activation energy

Answer 28

Chemical reactions can occur only when reacting particles collide with each other and with sufficient energy
- so it’s the minimum amount of energy that particles must have to react

Question 29

describe an endothermic reaction diagram

Answer 29

• the reactants have less energy than the products,
  because the energy has been taken in from the surroundings
• so activation energy will be more

Question 30

describe an exothermic reaction diagram

Answer 30

• the products have less energy than the reactants, because the energy has been released to the surroundings
• so activation energy will be less