rates of reaction and energy change Flashcards
(29 cards)
mean rate of reaction =
quantity of reactants used or product made / time taken
steep rate of reaction curve
high rate of reaction
happening quickly
shallow curve rate of reaction
reaction is happening slowly
change in mass method of rate of reaction
reaction mixture placed on balance
if a gas is produced, the mass will decrease as cottonwool allows gas to escape but not anything else
the mass of the mixture is recorded at regular time intervals
rate = change in mass / time
volume of gas produced method of rate of reaction
connected to gas syringe or upside down measuring cylinder
apparatus collects gas
volume of gas produced is recorded at regular time intervals
rate of reaction = volume of gas produced / time change
the minimum amount of energy required for a reaction to take place is the
activation energy
how does temperature affect rate
increased temp
particles have more energy
move faster
more frequent successful collisions
rate increases
how does pressure affect rate
increased pressure
particles more crowded
more frequent collisions
rate increases
how does concentration affect rate
increases concentration
particles more crowded
more frequent collisions
rate increases
how does surface area affect rate
increased surface area
increase number of reactant particles exposed
more frequent collisions
rate increases
how do catalysts affect rate
catalysts provide an ALTERNATIVE REACTION PATHWAY with a LOWER ACTIVATION ENERGY
so a greater proportion of particles will have energy exceeding the activation energy when they collide
more successful collisions
rate increases
enzymes
biological catalyst
important in industry - used in industrial reactions eg fermentation of sugars to make alcohol
presence of enzymes means these reactions can occur at lower temps and pressures
found in the single celled fungus yeast
chemical reactions which are accompanied by a change in heat energy
salt dissolving
displacement reactions
neutralisation reactions
precipitation reactions
when these happen in solution we can observe temp change using a thermometer
exothermic reactions
reaction that transfers energy to surroundings causing temp of surroundings to increase
combustion
oxidation
neutralisation
endothermic reactions
reaction that takes in energy from surroundings so temp of surroundings decreases
thermal decomposition
sodium hydrogen carbonate and citric acid
sports injury packs
how to investigate the variables that affect temperature change
30 cmcubed of hcl in polystyrene cup
put in beaker to stabilise
record initial temp using thermometer
record this
add 5 cm3 NaOH using measuring cylinder
add to polystyrene cup
add lid
stir
record max temp
repeat and find mean
repeat for different volumes of NaOH
independent variable
begins with I - what I changed
dependent variable
its what you measure
control variable
keep the same
sources of error when measuring temp change
unwanted heat transfer
the bigger the temp change.. the more
energy has been absorbed or released
reaction profiles
used to show the relative energies of reactants and products, the overall energy change and the activation energy
exothermic reaction profile
reactants at higher level then products
endothermic reaction profile
reactants at lower level than products
