Chemical Reactions
Reactants and products - New substances are formed with chemical reactions. The chemical substances which are changed are called the reactants and the new substances formed are called the products.
Collision Theory - For a chemical reaction to happen, the reactants must collide. The collision between the molecules provides the energy needed to break the bonds so that new bonds can form. The molecules must collide in a particular way, the place on the molecule where the collision must take place is called the reactive site.
Sometimes a collision may occur but not enough kinetic energy is available to be transfered. Raising the temperature can increase kinetic energy enabling bonds to become broken during collisions. The energy you supply to get a reaction going is called the activation energy.
Exothermic Reactions: Releasing heat - In this type of reaction, heat is released when you go from reactants to products. The reactants are in a higher energy state than the products.
Endothermic reactions: Absorbing heat - In this type of reaction, heat is absorbed. The reactants are in a lower energy state than the products.
Different types of chemical reactions occur based on; the identity of the reactants and products and which bonds are broken and made. Some common reactions include - combination, decomposition, single displacement, double displacement and reduction-oxidation (redox).
Combination reactions - two or more reactants form one product. e.g sodium and chlorine to form sodium chloride.
Decomposition reactions - Here a single compound breaks down into two or more simpler substances. These reactions are opposite of combination reactions. e.g the decomposition of water into hydrogen and oxygen gases.
Single Displacement reactions - A more active element displaces another less active element from a compound.e.g Putting zinc metal into copper sulfate solution, the zinc displaces the copper.
Double displacement reactions - Here two species (normally ions) are displaced. Usually an insoluble solid or water will be formed.
Things to remember; 1) If a compound is soluble, it will not react at all and can be represented by (Aq). 2) If a compound is insoluble, it will precipitate (form a solid).
Neautralization reactions - A reaction between an acid and a base occurs forming water.
Combustion reactions - When a compound (usually containing carbob) reacts with oxygen gas in air resulting in burning.
Redox reactions - reactions where electrons are exchanged. These types of reactions are found in combustion, photosynthesis and respiration.
Balancing chemical equations - the law of conservation of mass states matter is neither created nor destroyed. i.e atoms in an equation cannot be gained or lost - just combined differently. The same number should be present on both sides of the equation, it should be balanced.
Its a good idea to wait until the end to balance hydrogen and oxygen atoms.
Example 1 - N2(g) + H2(g) → NH3(g)
Lets start with the nitrogen atoms. There are 2 on the left and 1 on the right. In order to balance them, place a 2 infront of the NH on the left.
N2(g) + H2(g) → 2NH3(g)
For the hydrogen atoms, there are 2 on the left and 6 on the right (2x3). Put a 3 infront of the H2 on the left. which gives N2(g) + 3H2(g) → NH3(g)
