reaction rates

Question 1

ZXC what is the rate of reaction?

Answer 1

the number of moles of product formed per second

OR the amount of reactant used per second

Question 2

what is the unit for rate of reaction?

Answer 2

mol/s

Question 3

what are the 4 methods to measure rate of reaction?

Answer 3

mass change
volume of gas
solid disappearing
colour change

Question 4

what needs to be true to use the mass change method?

Answer 4

there has to be a gas used up or a gas made

Question 5

describe the apparatus for the mass change method

Answer 5

do the reaction in a conical flask
fill it with the reactants
put a piece of cotton wool on the top to prevent liquid leaving
measure the mass change using a balance every x seconds

Question 6

what does a gradient and tangent tell you?

Answer 6

gradient tells you the rate of reaction
tangent is a straight line that has the same gradient as one point on a curve

Question 7

describe the aparatus for the volume of gas method

Answer 7

based on displacement of water
can either use downward delivery or use a gas syringe
measure the volume of gas produced every x seconds

Question 8

describe the solid disappearing method

Answer 8

use for a reaction where there is a solid in reactants and aqueous in products
measure time until solid disappears

Question 9

what are the downsides of solid disappearing method?

Answer 9

you cannot make a graph
you can only calculate the average rate, not the rate at different points

Question 10

describe the colour change method

Answer 10

use for a reaction where there is a colour change from reactants to products
measure the time until the color change is observed

Question 11

what are the downsides of colour change method?

Answer 11

you cannot make a graph
you can only calculate the rate
it is subjective - exactly which point the colour changed at

Question 12

what is the trend observed over the course of the reaction in terms of the rate?

Answer 12

the rate ALWAYS DECREASES from the beginning to the end of the reaction

initial rate (0) is always the highest

Question 13

why does the rate decrease over the course of the reaction?

Answer 13

because the frequency of collisions decreases
the reactants are used up during the reaction, causing fewer to be available to react

at the end of the reaction there are no more reactants available so no more collisions can occur