calculating rates of reactions

how can you measure the rate of a reaction?

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

• rate = amount used or formed ÷ time

how do you measure the rate when products or reactants are gases or solids?

gases are measured in cm³, solids in grams (g).

what units are used to measure the rate of a reaction?

cm³/s, g/s, or mol/s

what is the first method for measuring the rate of a reaction?

precipitation and colour change

how does precipitation and colour change work?

you observe the visual change, like when a transparent solution becomes opaque due to precipitate or when a coloured solution becomes colourless

what are the problems with using precipitation and colour change to measure reaction rates?

it's subjective; people may disagree on when the mark disappears or colour changes. you also can't plot a rate graph

what is the second method for measuring the rate of a reaction?

change in mass (usually when gas is given off)

how does measuring change in mass work?

use a mass balance to measure the loss of mass as gas is released; the faster the drop in mass, the faster the reaction

what are the advantages of using a mass balance to measure the rate?

it’s accurate and allows you to plot a rate of reaction graph

what is the third method for measuring the rate of a reaction?

the volume of gas given off

how does using a gas syringe measure the rate?

measure the volume of gas released; more gas in a given time means a faster reaction

what are the advantages of using a gas syringe?

it's accurate, and you can plot a rate of reaction graph

what is a problem with using a gas syringe?

if the reaction is too vigorous, it may blow the syringe's plunger