Chemical Reactions

• Atoms are not created nor destroyed in a chemical reaction and all the atoms in the reactants are in the products, however, they are rearranged. The only thing that is changing is the bonds made and broken.

• No mass is lost or gained in a chemical reaction as no particles are added or removed.

• Chemical reactions do involve a change in energy, such as taking in or giving out different energies, such as heat, light or sound.

• Visible changes also occur in a chemical reaction. This can be a gas coming off, a solid being made or a colour change.

• The mass of a chemical reaction can decrease after a chemical reaction due to a gas coming off, however, you can prevent this from occurring by putting a balloon and collecting the gas in there.

Examples of Chemical Reactions

• There are three things necessary for combustion, which is burning using oxygen. You need fuel, heat (energy) and oxygen. Examples of fuels are hydrocarbons. A Hydrocarbon is just Hydrogen and Carbon together (CH4). Examples of hydrocarbons are oil, petrol and natural gas. Combustion is good as it gives off energy in the form of light and heat.

• Oxidation is another form of a chemical reaction. Oxidation is when a substance reacts and combines with oxygen. An example of this is when iron rusts, or even combustion.

• Thermal Decomposition is the breaking down of a singular substance into two or more different substances. They usually break down into a (metal) oxide and carbon dioxide. This chemical change is considered 'different’ as it is not reacting with anything and just breaking into different things. This results in a colour change.

More On Chemical Reactions

• Chemical reactions are irreversible.

• In an Exothermic reaction, heat energy is given out. This causes a rise in temperature. Examples of this are neutralisation reactions and oxidation reactions. In addition, condensing and freezing are exothermic reactions, as they are giving out their energy to be able to cool and then condense/freeze. You end with less energy than you had in the beginning. Exothermic reactions are much more common than Endothermic reactions. Handwarmers are exothermic.

• In an Endothermic reaction, heat energy is taken in. This causes a decrease in temperature. You end up with more energy than you started out with. This is much more uncommon than exothermic but examples can be thermal decomposition or sports injury packs.

• Catalysts increase the speed of a chemical reaction and they are not changed nor used up themselves and are reusable. Catalysts also decrease the minimum amount of energy required to start a reaction and lower the temperature needed to start the reaction.

• Catalysts help industries as they increase the speed of the reaction, lower the temperature needed, make reactions cheaper and they increase the number of products made in a given amount of time, however, they are expensive to buy and different reactions need different catalysts, and they can be poisoned and required to be cleaned.

Balancing Equations

• A word equation shows the names of the products and reactions names in full.

• A symbol equation shows the chemical symbols and how many of each molecule or atom there is.

• Chemical reactions are always balanced, however, you need to figure out how to balance them on paper.

• For example, Mg + O2 → MgO is not balanced, however, 2Mg + O2 → 2MgO is, and you need to know how to write it each time.

Acids and Alkalis

• Acids are a group of chemicals. They can be dangerous depending on where they are on the pH scale. Acids can burn through the skin. They taste sour.

• Alkalis are a group of chemicals. They can be dangerous depending on where they are on the pH scale. Alkalis can dissolve the skin. They taste bitter and are soapy and slimy.

• The pH scale goes from 0 to 14. 0 is really strong and so is 14. Alkali>7, Acid<7. This means that anything below a 7 is an Acid and anything above a 7 is an Alkali. 7 is neutral and most of the time is water. The further the pH number is from 7, the more dangerous it is.

• Litmus paper changes colour depending on whether something is an acid or alkali. Acids are red and Alkalis are blue. The universal indicator shows whether something is an acid or alkali and also shows the pH number which indicates how strong it is. The universal indicator liquid is similar.

• Rainwater is acidic due to pollution, and acid rain, which is just extremely polluted rain, has more acid.

• 0-3 on the pH scale is a strong acid, 4-6 is a weak acid, 7 is neutral, 8-10 is a weak alkali and 11-14 is a strong alkali. Warm colours are acids and cool colours are alkalis.

Neutralisation Reactions

• Acids react with Alkalis to make salt and water. There are many different types of salts, such as sodium chloride (table salt), copper sulfate, sodium nitrate and more.

• You can make salt using neutralisation reactions, and the way you do this is pretty easy. You add a few drops of an acid to the alkalis and every few drops, you take an indicator to see if the pH is neutral. Repeat this until it is neutral. When it is neutral, you can put it into an evaporating dish and around 2/3 of it will be boiled off and makes a saturated solution of the salt, which is when there is so much salt in the water, no more salt can be dissolved in it. Leave the solution overnight and salt crystals will begin to form. The slower the crystalization process is, the bigger the crystals will be.

• To get the salt you want, change the type of acid. For example. hydrochloric acid makes chloride salts, sulfuric acid makes sulfate salts and nitric acids make nitrate salts.