2.2.1 rate of reaction and measuring rates of reaction

what happens as a chemical reaction proceeds to conc of reactants and products

concentration of reactants decreases and concentration of products increases

what is the rate of reaction

speed at which a chemical reaction takes place

what is the units of rate of reaction

mol dm-3 s-1

what is the equation for rate of reaction

change in concentration of reactants or products / change in time

draw the rate of reaction graph for conc of reactants against time and conc of products against time

the steeper the gradient…

the faster the rate of reaction

how do we calculate the rate of reaction at a give time (instantaneous rate of reaction)

draw tangent to the curve at that time and cacluate the gradient of the tangent

how do we calculate gradient of tangent

gradient = change in y / change in x

what do we need to measure to measure the rate of reaction

how quickly the reactants are used up or how quickly the products are formed

why is the initial rate of reaction fastest

high concentration of reactant particles results in high frequency of collisions between reactant particles

why does the rate of reaction decrease with time

concentration of reactant particles decreases so decrease in frequnecy of collisions between reactant particles

what happens to the tangent when reaction is complete

tangent is horizontal

what are 3 ways of measuring rates of reaction

mass loss

gas production

colormetry

what is a colorimeter or spectrophotometer

measures the amount of light that passes through a solution

when can we use a colorimeter to measure rate of reaction

when a solution changes colour in a reaction

how does this work

light intensity that reaches a detector is measured and data plotted to show how conc of reactants or products changes with time

why can colorimetry not be used to monitor formation of coloured precipitates

light will be scattered or blocked by precipitate

what usually happens to a gas if produced in a reaction

is lost from the reaction vessel

what does this mean for the mass of the vessel

it decreases

how do we measure rate of reaction uses changes in mas

mass measured every few seconds and results plotted

what is a limitation of this method

the gas must be sufficiently dense or the change in mass is too small to measured on balance

how can we measure rates of reaction using changes in volume of gases

when gas produced, can be trapped and volume measured over time