Calculations Flashcards
Avogrado constant
The number of atoms in 12g of Carbon 12- 1 mole of anything else contains this number of particles.
6x10 ^23^ particles.
Moles (mass)
mass in grams
number of moles Molar mass(g/mol)
Moles (gasses)
volume of gas in cm^3
number of moles 24 000cm^3
Moles (liquids)
number of moles
concentration in mol/ dm3 Volume in dm3
Rate of reaction
Rate= Change of concentration of reactant
——————————————
time
Rate of reaction: Increase concentration
Increase in rate
Particle collision theory- more particles/ volume so more collisions so more successful collisions per second.
Rate of reaction: Increase temperature
Increase in rate
Particles have more energy- more collisions have the required activation energy
-more collisions happen because the particles move more faster.
Rate of reaction: Increase surface area
Increase in rate
More particles in contact with the other reactant and particles collide more often so more successful collisions per second.
Catalyst
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.
How catalysts work
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.
Activation energy
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.
Dynamic equilibrium
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.
Le Chatelier’s principle
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.
Effect of increasing the pressure
Equilibrium shifts in the direction that produces the smaller number of molecules of gas.
Effect of increasing the temperature
Equilibrium shifts in the endothermic direction
Exothermic reaction
- Heat is given out (EXplosion)
- Reaction gets cooler
- Making of bonds
__________
|
| heat evolved
v___________
Endothermic reaction
- Heat energy is taken in
- Reaction gets hotter
- Breaking of bonds
\_\_\_\_\_\_\_\_\_\_\_\_\_ ^ | heat absorbed \_\_\_\_\_\_\_\_\_\_\_|
Molar enthalpy change
ΔH represents enthalpy change for endo and exothermic reactions.
Negative enthalpy change
Exothermic, gives out heat
Positive enthalpy change
Endothermic, takes in heat
Percentage yield
Product output
—————– x 100
Product input
Titration
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.
Indicator used for titration
Methyl Orange
Concentration is measured in
mol/ dm ^-3
OR
grams/ dm ^-3
