Equations+and+Calculations

__ **Calculating Percentage Mass of and Element in a Compound** Relative mass of element in the compound__ X 100% Relative formula mass of compound

ExampleCalculate the percentage mass of magnesium in magnesium oxide, MgO

Relative mass of magnesium =24 Relative formula mass of MgO = 24 +16 = 40

24 /40 X 100% = 60%

__Calculating the Empirical Formula of a Compound__ The empirical formula of a compound is the simplest formula that represents the composition of the compound by mass.

__** Balancing Equations **__ In a perfect reaction the number of atoms in the reactants must be equal to the number in the product. Most equations don't show this, they only show the equations but not proportions.

__**Example**:__ H² + 02 = H²O (not balanced) 2 hydrogen 2 Hydrogen 2 oxygen 1 Oxygen As we see from the equation you must always a ractio of hydrogen to oxygen as 1:2 in water. To balance the equation you must maintain this ratio.

4 Hydrogen 4 Hydrogen 2 Oxygen 2 Oxygen As we see the ration of oxygen to hydrogen is 1:2 on both sides.
 * __Balanced:__** 2H² + 0 = 2H²0

__**Uses:**__ This equation tells us 1 mole of oxygen reacts with 2 moles of hydrogen to create two moles of water.


 * __ Proportion of elements/substances in reactions __**