topic 6: the rate and extent of chemical change

i love rates&equilibria <3

two ways to measure rate

• measure the rate at which a reactant is used up

• measure the rate at which a product is formed

factors affecting rate

• surface area

• temperature

• concentration

• pressure

how can you calculate rate? give one of its units?

• g/s OR cm³/s OR mol/s

for any reaction to occur, particles must:

• collide

• collide w sufficient energy

• (collide in the right way)

activation energy

minimum energy needed to get a reaction to start

collision theory

a reaction will only occur when reactant particles collide w each other

how does increasing the temperature affect rate?

• particles move faster

• more collisions

• more collisions which occur w enough energy to react

• more successful collisions

• rate increases

what is concentration?

measure of the number of particles in a given volume

how does increasing concentration affect rate?

• more reactant particles in the same volume

• greater chance of particles colliding

• more successful collisions

• rate increases

how does increasing SA affect rate?

• more particles exposed to other reactants

• more successful collisions

• rate of reaction increases

function of a catalyst

• speed up chemical reactions but don’t get involved in them or get used up

• provides an alternative pathway w/ a lower activation energy

(required) describe an experiment to show the effect of increasing concentration on rate

• measure a set volume of dilute sodium thiosulfate solution w/ a measuring cylinder and pour into the conical flask

• put the conical flask on a piece of paper w/ a black cross drawn on it

• measure a set volume of dilute HCl w/ measuring cylinder

• pour this acid into the flask and at the same time swirl the flask gently and start the stopwatch

• look down through the top of the flask and stop the stopwatch when the cross is no longer visible

• record the time it takes for the cross to disappear in seconds in a table

• repeat for different concentrations of sodium thiosulfate

what should be controlled in this experiment?

• volume of dilute HCl

• volume of sodium thiosulphate

what are the risks involved in this experiment? (i’m not sure if my answers are right it was just in the practical handbook)

• breathing in sulfur dioxide fumes

• breaking glassware and cutting yourself on it?

on a graph, how is the rate of reaction found? as this varies, what does it show?

• gradient - the larger the gradient, the higher the rate

• over time, the gradient will decrease as the reactants are used up

• the fastest reactions will have the largest gradients and become flat in the least time

factors affecting equilibria

pressure, temperature, concentration

when is equilibria established?

rate of forward reaction = rate of backward reaction, concentration of reactants and products remain constant

Le Chatelier’s Principle

if a change is made to a system at equilibrium and a change is made to any of the conditions, the system responds to counteract the change

how does an increase in pressure affect the equilibrium?

position of equilibrium shifts to the side w/ the fewer number of particles

how does an increase in temperature affect the equilibrium of a reaction?

position of equilibria shifts in the direction of the endothermic reaction

how does an increase in concentration of the reactants affect the equilibrium?

position of equilibrium shifts towards the products

how does an increase in concentration of the products affect the equilibrium?

position of equilibrium shifts towards the reactants

closed system

a system where no reactants or products can escape