Topic 7 - Rates of Reaction and Energy Changes Flashcards
Explain how reactions occur
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
What increases rate of reaction?
greater the frequency of collisions, greater the rate of reaction
explain how temperature affects rate of reaction
rate INCREASES when temp increases bc particles gain energy and:
- move faster
- frequency collisions increase and
- collision energy increases , more collisions successful
explain how concentration and pressure affects rate of reaction
rate INCREASES if concentration of dissolved reactant increases or pressure of gas reactant
- more particles in same volume
- successful collisions increases
explain how surface area:volume ratio affects rate of reaction
rate INCREASES when sa:v increases:
- more reactant particles available
- successful collisions increase
describe three features of a catalyst
catalysts - substances speed up rate without altering products.
unchanged chemically and in mass at end of reaction
explain how a catalyst works
catalysts provide alternative reaction pathway with lower activation energy
explain the use of enzymes
enzymes are BIOLOGICAL catalysts
used in the production of alcoholic drinks
explain the relationship between rate and time of reactions
the GREATER the rate, the LOWER the reaction time
- fast reaction in short time eg combustion
- slow reaction in long time eg rusting
explain effects of changes in heat energy
- salts dissolving in water (endo & exo)
- neutralisation reactions (endo & exo)
- displacement reactions (exo)
- precipitation reactions (endo & exo)
what is an endothermic reaction
heat energy TAKEN IN
reaction mixture or surroundings decrease in temperature
what is an exothermic reaction
heat energy GIVEN OUT
reaction mixture or surroundings increase in temperature
describe a method to measure temperature changes
thermometer, polystyrene cup, reaction mixture, lid with hole and beaker for support
beaker and air inside further insulation to reduce energy transfer
describe what happens in terms of bonding in endothermic vs exothermic
endothermic - breaking bonds (energy needed)
exothermic - making bonds (energy released)
bENDy mEXican
describe the overall heat energy trend in an endothermic reaction
- less heat energy released forming bonds in products than required breaking bonds in reactants
- positive energy change
- reactant energy level lower than product
describe the overall heat energy trend in an exothermic reaction
- more heat energy released forming bonds in products than required breaking bonds in reactants
- reactant energy level greater than product
- negative energy change
explain the term activation energy
energy needed to start a reaction
how to calculate energy change
energy change = total energy in - total energy out
if the final answer is a negative, reaction is exothermic
if positive, endothermic
why does oxygen gas have an extremely low boiling point
weak intermolecular forces
why do hotter acids react faster with calcium carbonate
higher temperature, quicker reaction
the particles move faster so more frequent collisions
why does powdered calcium carbonate react faster with acid than big lumps?
higher surface to volume ratio, quicker reaction
more places for them to collide
