Section 5 - Physical Chemistry

Question 1

Definition of exothermic reaction:

Answer 1

gives out energy to surroundings, usually as heat

Question 2

Definition of endothermic reaction:

Answer 2

takes energy from surroundings, there is a fall in temp in surroundings.

Question 3

Enthalpy change

Answer 3

change of temp in a reaction

Question 4

If reaction is exothermic enthalpy is . ..

Answer 4

negative, the reaction gives out energy

Question 5

If reaction is endothermic enthalpy is . …

Answer 5

positive, the reaction takes in energy

Question 6

Heat energy transferred equation:

Answer 6

Q = m x c x T

Question 7

exothermic reactions

Answer 7

• condensing
• freezing
• oxidation
• combustion
• neutralisation

Question 8

endothermic reactions

Answer 8

• melting
• boiling
• decomposition
• reactions of metals, hydrogen, carbonates + acids

Question 9

Calorimetry definition

Answer 9

change in heat of a substance

Question 10

Calorimetry formula

Answer 10

q=mcT

Question 11

Particle collision theory

Answer 11

• Particles are constantly moving
• Chemical reaction to take place the reactants first have to collide
• Amount of activation energy is different depending on the ocasion

Question 12

Activation energy definition

Answer 12

minimum amount of energy supplied to break bonds

Question 13

RoR definition

Answer 13

Change that involves rearranging atoms from reactant molecules to form new products

Question 14

RoR evidence

Answer 14

colour change, temp change, bubbles, precipitate formation

Question 15

RoR grams

Answer 15

Quantity of products formed / time taken (s)

Question 16

RoR cm(cubed)

Answer 16

quantity of reactants used / time taken (s)

Question 17

Factors to change the speed of a reaction

Answer 17

Concentration
Temperature
Pressure
Surface Area
Catalysts

Question 18

How does concentration affect?

Answer 18

• More particles in the same space means more collisions
• More collisions means more effective collisions
• If you double the concentration you double the number of collisions

Question 19

How does temperature affect?

Answer 19

• particles when heated gain kinetic energy
• When they move faster they collide more frequently

Question 20

How does surface area affect?

Answer 20

• Smaller particles increase surface area
• more collisions happen because particles are more likely to collide

Question 21

How does catalysts affect?

Answer 21

• reduce activation energy needed for a reaction
• less activation energy means more effective collisions
• They dont work on all reactions.

Question 22

Rate of chemical reaction depends on

Answer 22

• Collision frequency of reacting particles
• energy tranferred during a collision

Question 23

What is a reversible reaction?

Answer 23

products of a reaction can react with each other and convert back to the reactants

Question 24

Example of reversible reaction

Answer 24

thermal decomposition of ammonium chloride