Chemistry
Quantitative Chemistry
Exo and Endo
Mole calculations
Mass = Mr x Moles
Mr = Mass/Moles
Moles = Mass/Moles
Mass must be in grams
Mole ratio between molecules is the big numbers in the balanced equation
Concentration
Concentration = Mass/Volume
Volume has to be in (dm3)
Concentration is in g/dm3)
Concentration is a measure of how much solute is dissolved in a solution
Titrations
Titration is the slow addition of one solution of a known concentration (called a titrant) to a known volume of another solution of unknown concentration .
This is until the reaction reaches neutralisation, which is often indicated by a colour change
Equipment - Burette, Conical flask, White tile
Percentage Yield is the mass of the product you got by the product you expected to gain times by 100
Atom Economy is the mass of the product you want by the whole products gained times by 100
Ar and Mr
Ar is the Relative Atomic Mass of a element (Bottom Number an periodic table)
Mr is the Relative Molecular Mass, comes from the sum of the Ar of a molecuar
Converting Units
cm3 --> dm3 divide by 100
m3 to dm3 multiply by 100
Limiting reagents
The reactant is used up first and prevents more product from being made is the limiting regent
Substance that is in excess or doesn't get used up is the excess reagent
Volume of gases
Volume = Moles x 24
Volume has to be in (dm3)
24 is the molar volume, the volume that one mole occupies at room temperature
Cells and Batteries
In Non-rechargeable cells and batteries, the chemical reactions stop when one of the reactants has been used up. E.g Alkaline batteries
In rechargeable cells and batteries can be recharged because the chemical reactions are reversed when an external electrical current is supplied. Forcing the reaction the other way, therefore the electrons
Exothermic and Endothermic
Endothermic
Heat exits the reaction. The temperature outside goes down
Exothermic
Heat exits the reaction. The surrounding temperature goes up
Energy Profiles
Breaking bonds involves putting energy into the reaction
Wen bonds are made energy is released
Reaction Energy Diagram shows the energy at the start of the reaction and at the end
Reaction Pathway along with the activation energy is plotted between the reactants and products
Energy Bond Calculations
Bonds Broken-Bonds Made = Energy Change
Hydrogen Fuel Cells
At the Anode (positive), the Hydrogen oxides and produces Hydrogen ions. The electrons move along the circuit
At the Cathode (negative), the Oxygen reduces and gains the electrons creating the oxygen ions
The Hydrogen ions and Oxygen ions form an ionic bond to make water
4H+ + O2+4e-
Rates of Reaction - Speed at which reactants changed into products
Mean rate of reaction equation = quantity of reactants used/time
Mean rate of reaction equation = quantity of products formed/time
Collision theory
Reactions only take place when:
Particles come together
Have enough energy
To improve the rate of reaction
Increase the frequency of collisions between reacting particles
Increase energy they have when colliding
Catalysts - A catalysts speeds up the rate of reaction without being used up. Remains chemically unchanged
Provides an alternative reaction pathway with lower activation energy
Can be poisoned, so they stop workig
Reversible reactions and Equilibrium
A reversible reactions, if the forward reaction is exothermic, the reverse reactions will be exothermic
Equilibrium is when the rate of reaction of the formed reaction is equal to the rate of reaction of the backwards (reverse) in a reversible reaction.
This can only take place in a closesd system
Le Chateliers principle states that if a system at equilibrium is subjected to any change, the system will adjust to counteract change
Affected by
Temperature
Pressure
Concentration
Catalysts
Increase in temperature, favours endothermic as it takes in that energy
Increase, higher mole reacts so more of the other
Favours side with less moles
No basis just quicker
Decrease in temperature ,Favours exothermic
Increase concentration, higher mole reacts more due to more particles so more of the other
Increase, higher mole reacts so more of the other