Rates of reaction

Question 1

Rate of reaction formula

Answer 1

amount of reactant used or amount of product formed/time

Question 2

Describe an experiment of the reaction between marble chips and HCl

Answer 2

Products: Calcium chloride, water, carbon dioxide
CaCO3 chips in volumetric flask on a balance
Pour HCl into the flask, immediately place the cotton wool closing the top (allows CO2 to escape but stops acid spraying out)
Repeatedly measure the mass of CO2 lost (every 10 seconds) until the reaction has stopped and plot in a graph

Question 3

Experiment to investigate the effect of changes in surface area of solid:

Answer 3

Increase size of marble chips
-Rate of reaction decreases, although same amount of CO2 is produced as amount of CaCO3 has not changed
-Because Surface area is smaller, there are less particles exposed, less frequent collisions

Question 4

Experiment to investigate the effect of changes in concentration of solution (HCl)

Answer 4

Half the concentration of acid (marble chips must be in excess)
-Rate of reaction decreases, and volume of CO2 produced is halved as there are less particles in the same volume (of acid)
-Because less particles in same space, less frequent collisions

Question 5

Experiment to investigate the effects of changes in temperature

Answer 5

Increase temperature, everything else at the same quantities
-Rate of reaction increases, although same amount of CO2 is produced as amount of CaCO3 or HCL has not changed
-Because the particles gain more kinetic energy, more frequent collisions, + higher proportion of collisions are successful because collision energy >= to the activation energy

Question 6

Experiment to investigate the effects of the use of a catalyst on the rate of a reaction

Answer 6

Hydrogen peroxide -> water + oxygen
Manganese(IV) oxide can be used as a catalyst
The rate of reaction is measured by measuring the volume of oxygen produced at regular intervals using a gas syringe
-Rate of reaction increases with catalyst as it offers an alternative pathway with lower activation energy

Question 7

Experiment to investigate the reaction between varying concentrations of sodium thiosulfate and HCl

Answer 7

-> Sodium chloride + sulfur dioxide + sulfur + water
Conical flask placed above a cross - observe from above, until the cross disappears (as a precipitate of sulfur forms)
In order to change the concentration of sodium thiosulfate, the volumes of sodium thiosulfate and water are varied
!!!Total volume of solution must be kept constant to ensure depth of solution remains constant
SO2 gas is poisonous, so the experiment must be carried out in a well ventilated room

Question 8

Explain increasing SA of a solid

Answer 8

More particles exposed
More frequent collisions
Rate of reaction increases

Question 9

Explain increasing concentration of a solution or pressure of a gas

Answer 9

More particles in same space
More frequent collisions
Rate of reaction increases

Question 9

Explain increasing temperature

Answer 9

Particles have more kinetic energy
More frequent collisions
And a higher proportion of those collisions are successful because the collision energy >= activation energy
Rate of reaction increases

Question 10

Catalyst definition

Answer 10

A substance that increases the rate of a reaction, but is chemically unchanged at the end of a reaction
-by providing an alternative pathway with lower activation energy

Question 11

Experiment to investigate the effect of different solids on the catalytic decomposition of hydrogen peroxide solution

Answer 11

Different catalysts could be used to investigate which is the most effective in decomposing hydrogen peroxide
E.g. Manganese dioxide, Liver, Potato, Potassium iodide, Copper oxide, Sodium chloride
If a substance is not a catalyst, there will be no bubbles of oxygen produced
The better the catalyst, the quicker bubbles of oxygen are produced