Chemical reactions

Question 1

Describe the effect of concentration, particle size,
catalysts (including enzymes) and temperature on
the rate (speed) of reactions

Answer 1

Concentration:
- If increase -> no. of particles in a given volume increases -> increase no. of successful collisions -> rate increases
Catalysts:
- Speeds up the ROR but remains unchanged
Temperature:
- Temp increases -> particles gain more energy -> moves faster -> successful collisions -> rate increases
Particle size
- Smaller particle size -> larger surface area -> number of particles in contact with other reactant increases -> successful collisions -> rate increases

Question 2

Describe the role of light in photochemical
reactions and the effect of light on the
rate (speed) of these reactions

Answer 2

The rate of some reactions increase as the intensity of light increases. Photochemical reactions depend on light to be reacted. e.g. photosynthesis- the reaction between carbon dioxide and water in the presence of chlorophyll and sunlight (energy) to produce glucose and oxygen

Question 3

Describe the use of silver salts in

photography

Answer 3

a process of reduction of silver ions to silver

Question 4

Concept of equilibrium

Answer 4

• Equilibrium is when the rate of forward reaction is equal to rate of reverse reaction
• At equilibrium the reactants are continually being changed to products and opposite
• At eq, the concentration of reactants and products does not change

Question 5

Shifting equilibrium

Answer 5

• Concentration of reactant increases -> moves to right to form more products
• Concentration of product increases -> moves to left
• Increase in pressure moves to the side with less moles and opposite. If there are equal volumes/moles of gas on both sides -> pressure has no effect
• Exothermic reaction: temp increases -> favours reverse reaction (endothermic)
• Endothermic reaction: temp increases -> favours exothermic

Question 6

OILRIG

Answer 6

Oxidation Is Loss of electrons

Reduction Is Gain of electrons

Question 7

Identify redox reactions by changes in oxidation state and by the colour changes involved when using acidified potassium manganate(VII), and potassium iodide.

Answer 7

• Potassium manganate (VII)
  + Add it to solution containing iron(II) ions
  + Iron(III) ions formed => solution changes from light green to yellow because iron(II) ions are oxidised
  + Purple potassium manganate (VII) becomes colourless => only see colour of iron (III) ions
• Potassium iodide
  + Good reductant in acidic solution
  + Colour changes from colourless to brown
  + Can be used as a test for oxidants

Question 8

Oxidising agent (oxidant)

Answer 8

a substance that removes electrons or adds oxygen to another sunstance

Question 9

Reducing agent (reductant)

Answer 9

a substance that adds electrons or removes oxygen from another substance