topic 6 - rate and extent of chemical change Flashcards
whats the rate of a reaction
the rate at which the reactants get turned into products
slow reactions examples
- rusting of iron
typical rate reaction example
reaction btwn mag and acid - hydrogen bubbles
fast rate of reaction example,
explosions - fireworks
rate of reaction equation
products formed or reactants used cm^3 /time secs
what are the axis for a graph to show rate of reaction
time on x axis
mass of reactants or volume of products formed on Y
the collision theory
for particles to react they have to collide with each other with activation enegry and if there is less energy than this nothing will happen
what does the collision theory depend on
- amount of energy they have
- frequency of collision
4 factors that affect the rate of reaction
- temp
- concentration/pressure
- surface area
- catalyst
how does temperature affect the rate of reaction
- temp increases
- particles gain more energy
- move faster and collide more frequently
- higher rate of reaction
how does concentration or pressure affect the rate of reaction
if these increased there will be more particles per unit of volume there fore more frequent collision
how does SA affect the rate of reaction
increase rate of reaction bc higher frequency of collision
how does catalyst affect the rate of reaction
speeds up reaction but doesn’t get used up
- catalyst lowers activation energy by providing an alternative reaction pathway = higher proportion of successful collisions
how do you calculate the actual rate of reaction at a particular point
find the gradient
- draw a line up from the time to the curve
- draw a tangent here
- change in y over change in x
reversible reaction rates
the forwards and backward reactions can happen at different rates
what happens when the reversible reaction reaches equilibrium
- forward and backward reactions even out and exactly the same speeds
- the overallllll concentration of the products and reactions won’t change but doesn’t mean they are the same
where is the equilibrium with more products in reversible reactions
more products = lies to the right
where is the equilibrium with more reactants in reversible reactions
more reactants = lies to the left
when can eq only be reached
in a closed system - none of the reactants or products can escape
what are the energy changes in a reversible reaction
Has to be exothermic in one direction and endothermic in the other
whats the energy changes in the reaction of thermal decomposition of hydrated copper sulfate
hydrated copper sulfate <—> anhydrous copper sulfate + water
- forward is endothermic
- backward is exothermic
what are the 2 points in la chatelier’s principle
- if you change the conditions of a reversible reaction at eq - the system will counteract that change
- therefore you can predict the effect of changes you make to a system
a chatelier’s principle - changing TEMP
- decrease temp = eq goes to the exothermic side.
- increase temp = eq goes to endothermic side.
a chatelier’s principle - changing PRESSURE
GASES
- increase the pressure = eq tries to reduce and moves in direction with less moles of gas
- decrease pressure = eq tries to increase and moves direction with more mole of gas
a chatelier’s principle - changing CONCENTRATION
- if you change the concentration the system is no longer at eq
- increase the conc of REACTANTS = system tries to decrease and makes more products
- decrease the conc of reactant = system tries to increase and reduces amount of reactants
