Calculations

Question 1

Avogrado constant

Answer 1

The number of atoms in 12g of Carbon 12- 1 mole of anything else contains this number of particles.

6x10 ^23^ particles.

Question 2

Moles (mass)

Answer 2

mass in grams

number of moles Molar mass(g/mol)

Question 3

Moles (gasses)

Answer 3

volume of gas in cm^3

number of moles 24 000cm^3

Question 4

Moles (liquids)

Answer 4

number of moles

concentration in mol/ dm3 Volume in dm3

Question 5

Rate of reaction

Answer 5

Rate= Change of concentration of reactant
——————————————
time

Question 6

Rate of reaction: Increase concentration

Answer 6

Increase in rate

Particle collision theory- more particles/ volume so more collisions so more successful collisions per second.

Question 7

Rate of reaction: Increase temperature

Answer 7

Increase in rate

Particles have more energy- more collisions have the required activation energy
-more collisions happen because the particles move more faster.

Question 8

Rate of reaction: Increase surface area

Answer 8

Increase in rate

More particles in contact with the other reactant and particles collide more often so more successful collisions per second.

Question 9

Catalyst

Answer 9

A substance that increases the rate of the reaction but is chemically unchanged at the end of the reaction. They can change during, but remain a catalyst as long as they return to how they were before.

Question 10

How catalysts work

Answer 10

They provide an alternative pathway for the reaction that has a lower activation energy than the original pathway. This means that more of the collisions taking place will have the necessary activation energy so more successful collisions per second.

Question 11

Activation energy

Answer 11

In order for anything to happen when particles collide, they need to have a minimum amount of energy to react with, called the activation energy.

Question 12

Dynamic equilibrium

Answer 12

If a reversible reaction is carried out in a closed reaction container, then it can (not always) reach a position of dynamic equilibrium, where both reactions (forward and backward) are still occurring. When the rate of both reactions is equal, the reaction is in dynamic equilibrium.

Question 13

Le Chatelier’s principle

Answer 13

If a chemical system at equilibrium experiences a change in concentration, temperature, volume, or partial pressure, then the equilibrium shifts to counteract the imposed change and a new equilibrium is established.

Question 14

Effect of increasing the pressure

Answer 14

Equilibrium shifts in the direction that produces the smaller number of molecules of gas.

Question 15

Effect of increasing the temperature

Answer 15

Equilibrium shifts in the endothermic direction

Question 16

Exothermic reaction

Answer 16

• Heat is given out (EXplosion)
• Reaction gets cooler
• Making of bonds

__________
|
| heat evolved
v___________

Question 17

Endothermic reaction

Answer 17

• Heat energy is taken in
• Reaction gets hotter
• Breaking of bonds

                \_\_\_\_\_\_\_\_\_\_\_\_\_
               ^
               |   heat absorbed \_\_\_\_\_\_\_\_\_\_\_|

Question 18

Molar enthalpy change

Answer 18

ΔH represents enthalpy change for endo and exothermic reactions.

Question 19

Negative enthalpy change

Answer 19

Exothermic, gives out heat

Question 20

Positive enthalpy change

Answer 20

Endothermic, takes in heat

Question 21

Percentage yield

Answer 21

Product output
—————– x 100
Product input

Question 22

Titration

Answer 22

Is about finding out exactly how much of two solutions you need to neutralise each other. When the indicator changes colour you are at the END POINT of the titration. Having found out how much acid and alkali (in burettte) is needed, you can make a pure solution of the salt but without the indicator.

Question 23

Indicator used for titration

Answer 23

Methyl Orange

Question 24

Concentration is measured in

Answer 24

mol/ dm ^-3
OR
grams/ dm ^-3