Topic 7 - Rates of Reaction and Energy Changes

Question 1

Explain how reactions occur

Answer 1

for a reaction to happen:

• reactant particles must collide
• collisions must have enough energy

ACTIVATION ENERGY - minimum energy needed by reactant particles for reaction to happen, successful collisions have this

Question 2

What increases rate of reaction?

Answer 2

greater the frequency of collisions, greater the rate of reaction

Question 3

explain how temperature affects rate of reaction

Answer 3

rate INCREASES when temp increases bc particles gain energy and:

• move faster
• frequency collisions increase and
• collision energy increases , more collisions successful

Question 4

explain how concentration and pressure affects rate of reaction

Answer 4

rate INCREASES if concentration of dissolved reactant increases or pressure of gas reactant

• more particles in same volume
• successful collisions increases

Question 5

explain how surface area:volume ratio affects rate of reaction

Answer 5

rate INCREASES when sa:v increases:

• more reactant particles available
• successful collisions increase

Question 6

describe three features of a catalyst

Answer 6

catalysts - substances speed up rate without altering products.

unchanged chemically and in mass at end of reaction

Question 7

explain how a catalyst works

Answer 7

catalysts provide alternative reaction pathway with lower activation energy

Question 8

explain the use of enzymes

Answer 8

enzymes are BIOLOGICAL catalysts

used in the production of alcoholic drinks

Question 9

explain the relationship between rate and time of reactions

Answer 9

the GREATER the rate, the LOWER the reaction time

• fast reaction in short time eg combustion
• slow reaction in long time eg rusting

Question 10

explain effects of changes in heat energy

Answer 10

• salts dissolving in water (endo & exo)
• neutralisation reactions (endo & exo)
• displacement reactions (exo)
• precipitation reactions (endo & exo)

Question 11

what is an endothermic reaction

Answer 11

heat energy TAKEN IN

reaction mixture or surroundings decrease in temperature

Question 12

what is an exothermic reaction

Answer 12

heat energy GIVEN OUT

reaction mixture or surroundings increase in temperature

Question 13

describe a method to measure temperature changes

Answer 13

thermometer, polystyrene cup, reaction mixture, lid with hole and beaker for support

beaker and air inside further insulation to reduce energy transfer

Question 14

describe what happens in terms of bonding in endothermic vs exothermic

Answer 14

endothermic - breaking bonds (energy needed)
exothermic - making bonds (energy released)

bENDy mEXican

Question 15

describe the overall heat energy trend in an endothermic reaction

Answer 15

• less heat energy released forming bonds in products than required breaking bonds in reactants
• positive energy change
• reactant energy level lower than product

Question 16

describe the overall heat energy trend in an exothermic reaction

Answer 16

• more heat energy released forming bonds in products than required breaking bonds in reactants
• reactant energy level greater than product
• negative energy change

Question 17

explain the term activation energy

Answer 17

energy needed to start a reaction

Question 18

how to calculate energy change

Answer 18

energy change = total energy in - total energy out

if the final answer is a negative, reaction is exothermic
if positive, endothermic

Question 19

why does oxygen gas have an extremely low boiling point

Answer 19

weak intermolecular forces

Question 20

why do hotter acids react faster with calcium carbonate

Answer 20

higher temperature, quicker reaction

the particles move faster so more frequent collisions

Question 21

why does powdered calcium carbonate react faster with acid than big lumps?

Answer 21

higher surface to volume ratio, quicker reaction

more places for them to collide