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equation for mean rate of reaction
total amount of products/ reactants (g or cm³) / time taken (s)
dm³ → cm³
multiply by 1000
what 4 conditions can increase the rate of reaction?
how does higher temperatures increase the rate?
increase surface area
high temperature
high concentration
high pressure
more kinetic energy causes more successful collisions
why do smaller objects such as powders increase the rate of reaction?
have a larger surface area to volume ratio,
so more collisions of particles take place
collision theory
chemical reactions can only occur when particles collide with enough energy
activation energy
the minimum amount of energy used by particles so they react
catalyst
substances which increase rate of chemical reaction by providing an alternative reaction pathway with a lower activation energy
how can the student investigate how the rate of reaction when the concentration of is changed by measuring the volume of gas produced?
use 50cm³ of 1mol/dm³ hydrochloric acid
use 3cm magnesium ribbon
set up a conical flask containing 50cm³ of 1mol/dm³ hydrochloric acid
have bung and delivery tube attached to gas syringe prepared
add a 3cm piece of magnesium ribbon
quickly fit bung on conical flask and start a stopwatch
record the measurement of gas produced every 10 seconds
repeat experiment with 2 and 3 mol/dm³ hydrochloric acid
how can the student investigate how the rate of reaction when the concentration of is changed by observing change of colour or turbidity?
use 10cm³ sodium thiosulfate solution
use 10cm³ dilute hydrochloric acid
pour 10cm³ of sodium thiosulfate solution into a conical flask
measure out 40cm³ water with a measuring cylinder and pour into conical flask
add 10cm³ dilute hydrochloric acid into conical flask and place it on a black cross and start a stopwatch
record the time it takes for the cross to disappear
repeat using other concentrations of sodium thiosulfate
reversible reaction
a reaction were the products can also form the reactants. If one direction is exothermic, the other one is always endothermic
exothermic
transfers energy to the surroundings
endothermic
takes in energy from surrounding
equilibrium
when the forward and backward reaction in a reversible reaction happen at the same rate in a sealed container
le chatelier’s principle
when a change of conditions happens to a system at equilibrium, the position of equilibrium moves to cancel out the change
If the concentration of a system at equilibrium is increased, what happens to the equilibrium?
equilibrium shifts to opposite side of substance which has increased concentration
If the concentration of a system at equilibrium is decreased, what happens to the equilibrium?
equilibrium shifts to the side of substance which has decreased concentration
(for gaseous reactions)
If the pressure of a system at equilibrium is increased, what happens to the equilibrium?
the equilibrium position will shift towards the side with the smaller number of molecules
(for gaseous reactions)
If the pressure of a system at equilibrium is decreased, what happens to the equilibrium?
the equilibrium position will shift towards the side with the larger number of molecules
If the temperature of a system at equilibrium is increased, what happens to the equilibrium?
equilibrium shifts to the endothermic side to increase products
the products at the exothermic side decrease
If the temperature of a system at equilibrium is decreased, what happens to the equilibrium?
equilibrium shifts to the exothermic side to decrease products
the products at the endothermic side increase
The equilibrium mixture is cooled.
Explain what happens to the concentration of the pink cobalt compound. [3]
concentration increases
because equilibrium moves to the left
because the reverse reaction is exothermic
Suggest why a catalyst is used in this industrial process.
Do not give answers in terms of increasing the rate of reaction. [1]
lowers energy costs
Suggest the effect of using the catalyst on the equilibrium yield of methanol. [1]
catalysts don’t effect the yield
what is meant by a closed system?
a system where the reactants or products cannot escape or enter