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