rate and extent of chemical change Flashcards
what is the rate of chemical reaction
speed at which reactants turn into products
what are common, medium and really fast reactions
slow-rusting which can take years
medium-mg + acid which produces gentle stream of hydrogen bubbles
really fast
fast-fireworks-happen in only fraction of second
what are 2 ways we can measure rate
how fast reactants are used
how fast products are formed
what are the equations for mean rate of reaction(cm3/s)or(g/s)
=quantity of reactants used(cm3) or products formed( g) divided by time(s)
what 4 factors affect rate of chemical reactions
temp
catalyst
pressure or conc
surface area
what is collision theory
for particles to react they must collide with activation energy
what factors affect rate of reaction
-temp
-sa
-conc/pressure
-catalyst
what happens when particles collide with less energy than activation
no reaction occurs and they just bounce back
what 2 things does collision freq depend on
-energy particles have-the more energy they transfer in collision
-collision frequency-more sucessful collisions
explain in 3 steps how inc temp affects rate of reaction
increases ke of particles
so they collide with more energy more frequently so more likely to exceed activation energy
this increases rate of sucessful collisions so higher rate of reaction
explain in 3 steps how conc/pressure affects rate of reaction
-more particles per unit volume so more frequent collisions increasing rate of reaction
what is the diff between conc and pressure
conc is for solutions
pressure is for gases
how does increasing sa affect rate of reaction
increases sa:volume ratio
so higher area for collisions with other reactants could take place
-increasing coll freq
-increasing rate of reaction
explain how we can measure effect sa has on rate of reaction
using a block/small chunks or powder of magnesium
with same volume and mass
how can we see how catalysts work
using reaction profile
what does a catalyst do
-provides alternate reaction pathway with lower activation energy so higher proportion of successful collisions
what are common catalysts
transition metals(eg nickel/cobalt
model answer
Particles will have more energy
Particles will collide more frequently
More successful collisions
Higher rate of reaction
what is the problem with using reactants used up/time taken
only finds mean rate of reaction while in reality it would have been faster at the start and slowed as progress
how can we track actual rate of reaction
by using graph with vol of product formed /reactant used on y axis and time in mins on x
what does finding the gradient on a reaction graph give us
rate of a reaction at a specific time
describe the reaction graph for reactants
model answer
The line is steepest at the start of a reaction because there are a lot of reactants
Over time, the line becomes less steep as the reactants are used up
At the end of the reaction, when all the reactants have been used up, the line plateaus.
what do forward and backwards reactions in reversible reactions tell us
forward is that reactants can turn to products
backwards is that products can turn to reactants
what is it when forward and backward reactions are the same
reactions are in equilibrium
what happens to products and reactants conc in equilibrium
conc of reactants and products wont change as they are forming each other at the same rate/cancelling out/constant
what must a reaction be in to reach equilibrium
a closed system so no reactants or products could escape
what are the arrows in reversible reactions representing
exothermic and endothermic
state le chateliers principle
changing conditions of reversible reactions will make the equilibrium position shift to try counteract change
what happens when pressure in a reversible reaction is increased
equilibrium moves to side with least gas particles(moles) and vice versa
what is an example of a reversiblereaction
the haber process
hydrogen+nitrogen—->ammonia
