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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Energy Transfer in Reactions

An exothermic reaction is one which gives out energy to the surroundings, usualy in the form of heat, which is shown by a rise in temperature.

Bond formation is an exothermic process.

In an exothermic reaction, the energy released in bond formation is greater than the energy used in breaking olds bonds.

An endothermic reaction is one which takes in energy from the surroundings, usually in the form of heat, which is shown by a fal in temperature.

Bond braking is an endothermic process

In an endothermic reaction the energy required to break old bonds is greater than the energy released when new bonds are formed.

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Measuring the Energy Content of Fuels

Use Specific Heat Capacity to calculate energy transfered:
Energy = mass x SHC x temp change

To meaure the energy given out per gram of fuel use:

Energy given out per gram = Energy released (in J) / Mass of fuel burned (in g)

          ( in J/g)

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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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Atom Economy

The atom economy of a reaction tells you how much of the mass of the reactants is wasted when manufacturing a cheical.

Atom economy = total relative formula mass of desired products / total relative formula mass of all products x 100

100% atom economy means that all the atoms in the reactants have been turned into useful products. The higher the atom economy the 'greener' the process.

High Atom Economy is better for Profits and the Environment

a) Reactions with low atom economy use up resources very quickly. At the same stime, they make lots of waster materials that have to be disposed of somehow.
b) Low atom economy reactions aren't usually profitable.
c) The best way aroudn the problem is to find a use for the waste products rather than just throwing them away.

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Percentage Yield

Percentage yield tels you about the overall success of an experiment. It compares what you think you should get (predicted yield) with what you get in practice (actual yield).

Percentage yield is give by the formula:

percentage yield = actual yield (grams) / predicted yield (grams) x 100

Yields are always less than 100%
Factors that cause this:
a) evaporation
b) not all reactants react to make a product
c) Filtration - when you filter a liquid to remove solid particles, you always lose a bit of liquid
d) Transferring Liquids

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Chemical Production

Batch Production
Pharmaceutical drugs are complicated to make ad there's fairly low demand for them. Batch production is often the most cost-effective way to produce small quantities of different drugs to order because:
1) It's flexible
2) Low start up costs
Disadvantages:
1) It's labour intensive
2) It can be tricky to keep the same quality from batch to batch

Continuous Production
Large-scale industrial manufacture of popular chemicals e.g. the Haber process
1) Production never stops so no time wasted
2) It runs automatically
3) The quality of the product is very consistent
However start-up costs to build the plant are huge

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Allotropes of Carbon

Diamond
Diamonds are lustrous(sparkyl) and colourless.
Each carbon atome forms four covalent bonds in a very rigid giant covalent structure, with makes diamond really hard.
All those strong covalent bonds take a lot of energy to break and give diamond a high melting point.Another example is graphite, has layers make up of atoms with 3 covalent bonds.

-Diamond and Graphite are Giant Molecular Structures

Fullerenes are Nanopartiles

1) Fullerenes are molecules of carbon, shaped like closed tubes or hollow balls.
2) Fullerenes can be used to 'cage' molecules. The fullerene structure froms around another atom or molecule, which is then trapped inside. This could be a new way of delivering a drug into the body, e.g. for slow release.
3) Fullerenes can be joined together to form nanotubes.

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