Physical chemistry - IGCSE

Question 1

Activation energy

Answer 1

The minimum amount of energy that particles must collide with to react

Question 2

Rate of reaction

Answer 2

The measure of the amount of product formed or reactant used over time

Question 3

Enthalpy change

Answer 3

The amount of heat energy given out or absorbed during a reaction

Question 4

Molar enthalpy change

Answer 4

The amount of heat energy given out or absorbed by one mole of a substance during a reaction
It can be calculated from a heat energy change
The value is made negative if the reacrion was exothermic

Question 5

Heat energy change

Answer 5

The energy change of a reaction which can be calculated from a calorimetry experiment as follows:
Q=mc(delta)t

Question 6

Calorimetry

Answer 6

The process used to measure the amount of heat energy released or absorbed during a chemical reaction

Question 7

Reaction profile

Answer 7

Graphs used to show the relative energies of reactants and products, the activation energy and the overall energy change of a reaction

Question 8

Catalyst

Answer 8

Increases the rate of reaction by providing a different reaction pathway with a lower activation energy
They aren’t used up during the reaction

Question 9

Dynamic equilibrium

Answer 9

Reached by reversible reactions when the rate of the forward reaction is equal to the rate of the backwards reaction
At dynamic equilibrium, the concentration of reactants and products remains constant

Question 10

Reversible reaction

Answer 10

A reaction in which the products can react together to reform the reactants

Question 11

Endothermic reaction

Answer 11

A reaction in which energy is taken in from the surroundings so the temperature of the surroundings decreases
Bond breaking is an endothermic process

Question 12

Exothermic reaction

Answer 12

A reaction in which energy is transferred to the surroundings so the temperature of the surroundings increase
Bond making is an exothermic process

Question 13

Neutralisation

Answer 13

The reaction in which an acid and a base react together to form a salt and water

Question 14

Effect of concentration on reaction rate

Answer 14

Increasing the conc of reactants in solution means the reacting particles will be closer together
They will collide more often so there will be a higher rate of successful collisions and a faster rate of reaction

Question 15

Effect of pressure on equilibrium

Answer 15

Increasing the pressure causes the equilibrium position to shift towards the side with the less moles of gas
Decreasing the pressure causes the equilibrium to shift towards the side with the larger number of moles of gass

Question 16

Effect of pressure on reaction rate

Answer 16

Increasing the pressure of gaseous reactants means the reacting particles will be closer together
They will collide more often so there will be a higher rate of successful collisions and a faster rate of reaction

Question 17

Effect of surface area on reaction rate

Answer 17

Increasing the surface area of the reactants means there are more exposed reacting particles
This means there are more frequent successful collisions, so the rate of reaction increases

Question 18

Effect of temperature on equilibrium

Answer 18

An increase in temperature will shift the equilibrium position in the direction of the endothermic reactions
A decrease in temperature will shift the equilibrium position in the direction of the exothermic reaction

Question 19

Effect of temperature on reaction rate

Answer 19

Increasing the temperature means the particles will have more kinetic energy and so will move faster
If the molecules are moving faster they will collide more often and, since they’ve gained kinetic energy, a larger proportion of the particles will have at least the activation energy
For both these reasons the rate of reaction increases