2Y: Chemical Reactions

A chemical reaction is a change that results in the formation of one or more new substances. When a chemical reaction has occurred, we could also say that a chemical change has taken place, that is, the reactants have been changed into products

Word equations and Chemical equations. iron + sulfur –> iron sulfide Fe + S –> FeS

During a fireworks display, magnesium is burned to give a very bright light. Let’s write a balanced equation for this reaction: magnesium + oxygen = magnesium oxide Mg + O2 = MgO Two magnesium atoms take part in a balanced reaction, so the final balanced equation is: 2Mg + O2 = 2MgO

The law of conservation of mass states that when a chemical reaction occurs, the total mass of the reactants is always equal to the total mass of the products. The word conservation means ‘staying the same’.

The term rate of reaction is used to describe how quickly chemical reactions occur. The rate of reaction is defined as the change in concentration per unit time of any one reactant or product. Rate of reaction = • Change in concentration of any one reactant or product / Time taken

A catalyst is a substance that alters the rate of a chemical reaction but is not used up in the reaction.

By experiment it is found that the rate of a reaction depends on five factors: • Types of reactants • Particle size • Concentration • Temperature • Catalysts

Review Experiments in Book.

A biochemical reaction is a chemical reaction that takes place in living cells, that is, a reaction in which new substances are formed. Examples: • Cellular respiration: where molecules such as glucose undergo biochemical reactions to release energy. • Photosynthesis: where carbon dioxide and water react to form glucose molecules in green plants. • Digestion: where large food molecules are broken down into other substances that can be used by our bodies.

The reactants are the chemicals that react together in a chemical reaction.

The products are the chemicals that are produced in a chemical reaction.