Percent Yeild

In doing stoichiometry calculations, we assume things do not go wrong (there is no error). In real terms this assumption is unrealistic. No reaction is going to proceed perfectly. When an equation is used to calculate the amount of product that will form in a reaction, then the value obtained is called the theoretical yield.

By contrast the amount of product that forms when a reaction is carried out in a laboratory is called the actual yield. The percent yield therefore is a ratio of actual yield to the percent yield. The percent yield is therefore a ratio of the actual yield to the percent yield.

Percent yield = (Actual yield/Theoretical yield) x 100

Limiting Reagents

As the name implies, limiting agents limits or determines the amount of product that can be formed in a reaction. The reaction proceeds until the limiting agent is used up. Then the reaction stops. The opposite of the limiting reagent is the excess reagent. The quality of an excess reagent, is more than enough to react with a limiting reagent.

Moles

In chemistry we measure quantities in many ways. We measure mass in Kg, volume in litres or cm3, for chemical quantities we also use the mole. A mole represents a number of particles. This is a very large number. This number is 6.02E23, and known as Avogadro's number. So a mole in chemistry represents Avogadro's number particles of any given substance.

The mole is one of the seven SI units, and it is represented by the symbol 'n' when used in a mathematical formula. We understand that matter is made of different kinds of particles, so the term representative particles refers to either atoms, ions or molecules.

Molecular mass

Mole = Mass/Molecular Mass

Measured in g/Mol
E.g. H2O 1+1+16 = 18g/Mol

Volume of a Mole of gas

Mole = Particles/Avogadro's number

The volume of a mole of gas is more predictable than the volume of a mole of a liquid or a solid. The volume of a mole of gas is usually measured at Standard Temperature & Pressure (STP).
Standard temperature is: 0° (273K) and
Standard pressure is: 1 Atmosphere (atm), 760mmHg or 103.8Kpa
At STP, one mole of a gas occupies a volume of 22.4 litres. This quantity of 22.4 litres is also know as the molar volume of gas.

Mole = Volume (litres)/22.4 litres

Balancing Equations

In every balanced chemical equation, each side of the equation (reactants and products) has the same number of atoms of each element on each side.

Rules of Balancing
1. Determine the correct formula for all the reactants and products involved.
2. Write the reactants on the left, and the products on the right.
3. Count the number of atoms of each element in the reactants and products.
4. Balance elements one at a time by adding coefficients to the front of the formulas.
*when there is no coefficient, it is assumed there is an invisible 1.
5. Check each atom to be sure the equation is balanced.
6. Make sure all coefficients are the smallest whole number ratio.

Acids

Acids are compounds that give off hydrogen ions when dissolved in water.

E.g. Hydrochloric Acid:

H+ + Cl- Water HCl

The formula for writing acids usually includes: Hx, where 'x' is a mono-atomic or polyatomic anion and H is Hydrogen.

Common acids are:

Acids

Acids are compounds that give off hydrogen ions when dissolved in water.

E.g. Hydrochloric Acid:

H+ + Cl- Water HCl

The formula for writing acids usually includes: Hx, where 'x' is a mono-atomic or polyatomic anion and H is Hydrogen.

Common acids are:

Covalent compounds aka Molecular compounds, are formed from non-metals that share electrons. Because there are many sharing between two non-metals, the formula cannot be guessed unless we have a naming system that reveals the atoms involved.

For this we use a set of prefixes:

">

The only time we drop a prefix is if the mono is to appear at the beginning of the name.

E.g. CO = Carbon Monoxide

CO2 = Carbon Dioxide *Note we don't say 'mono carbon'.

This doesn't work for metals, only non-metals. There last element changes to an 'ide'.