Chemistry C3

Atoms, Molecules and Compounds

Atoms
- Have a nucleus which is positively charged, and electrons which are negatively charged.
- Atoms can form bonds to make molecules or compounds, sometimes an atom loses or gains one or more electron and this gives it a charge (positive if it loses an electron, negative if it gains)
Charged atoms are known as ions, if a positive ion meets a negative ion they'll attract and from an ionic bond.
Covalent bonds are when non-metal atoms combine by sharing electrons.

Formulas to remember
1) Carbon dioxide        2) Hydrogen
3) Water                     4) Hydrochloric acid
5) Calcium chloride      6) Carbon Monoxide
7) Magnesium chloride 8) Calcium Carbonate
9) Sulfuric acid           10) Magnesium sulfate

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Chemical Reaction Rates

To get the rate of reaction you can:
a) Measure the change in mass - the mass will fall as the gas is released
b) Measure the volume of gas given off
Plotting these on a graph will show you the rate of reaction

The rate of a chemical reaction depends on:

  • How often they collide - the more collisions there are the faster the reaction is
  • The energy transferred during a collision - particles have to collide with enough energy to be successful

More Reactant used means more Product formed

1) The yield depends on the amount of reactant you start with
2) More reactant means more particles, these particles go on to have more reactions creating more product
3) If there is reactant left the reactant is in "excess"

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Collision Theory

More collisions increase the rate of reaction

4 Factors Increasing Collisions

1) Increasing the temperature means the particles are going faster and have more energy.
2) Increasing the concentration (or pressure) means the particles are more crowded together.
3) Smaller solid particles (or more surface area) means other particles can get to it more easily
4) A catalyst increases the number of successful collisions

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Reacting Masses

Relative Atomic Mass
Bigger number in the periodic table

Relative Formula Mass
Adding up all the relative atomic masses

Mass is Always Conserved
a) During a chemical reaction no atoms are destroyed and no atoms are created.
b) This means there are the same number and types of atoms on each side of a reaction equation.
c) By adding up the relative formula masses on each side of an equation you can see that no mass is lost

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Calculating Masses in Reactions

3 Key Steps
1) Write out the balanced equation
2) Work out Relative Formula Mass
3) Apply the rule: Divide to get one, then mutiply to get all

Example
1) 2Mg + Ov2 --> 2MgO
2)  2 x 24 = 48 --> 2 x (24 + 16) = 80
              48  --> 80
3) 48g of Mg reacts to give 80g of MgO
    1g  of Mg reacts to give       ?
  *60g*of Mg reacts to give       ?               *amount will be stated in question

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