PRESTWICK ACADEMY Chemistry department National 5 Unit 1 – Rates of Reaction Notes Revision of prior knowledge Chemical reactions When a chemical reaction takes place, a new substance is always formed. We can detect changes that show a chemical reaction has taken place. Eg. Colour change – Iron rusting, making toast Gas given off – An alka seltzer added to water Precipitate - When a solid is formed Energy changes also take place: – burning a candle. Heat – adding acid to alkali. These energy changes can be either exothermic or endothermic. Exothermic When a candle heat energy is given out. (the heat EXITS the reaction) This is known as an EXOTHERMIC reaction. In an exothermic reaction, energy is released to the surroundings, causing the surroundings to heat up. The products have less energy than the reactants because some of the energy has been released. Endothermic Here, energy is taken in from the surroundings (the heat ENTERS the reaction). The surroundings lose heat (cool down). So, in an endothermic reaction, the temperature falls. The products have more energy than the reactants because they have taken in extra energy from the surroundings. The speed of reactions Chemical reactions take place at different speeds (RATES). Some reactions are very fast like a firework going off; others are very slow like the forming of coal. The majority of reactions rates lie between these 2 examples.
PRESTWICK ACADEMY Chemistry department National 5 Unit 1 – Rates of Reaction Notes Revision of prior knowledge Chemical reactions When a chemical reaction takes place, a new substance is always formed. We can detect changes that show a chemical reaction has taken place. Eg. Colour change – Iron rusting, making toast Gas given off – An alka seltzer added to water Precipitate - When a solid is formed Energy changes also take place: – burning a candle. Heat – adding acid to alkali. These energy changes can be either exothermic or endothermic. Exothermic When a candle heat energy is given out. (the heat EXITS the reaction) This is known as an EXOTHERMIC reaction. In an exothermic reaction, energy is released to the surroundings, causing the surroundings to heat up. The products have less energy than the reactants because some of the energy has been released. Endothermic Here, energy is taken in from the surroundings (the heat ENTERS the reaction). The surroundings lose heat (cool down). So, in an endothermic reaction, the temperature falls. The products have more energy than the reactants because they have taken in extra energy from the surroundings. The speed of reactions Chemical reactions take place at different speeds (RATES). Some reactions are very fast like a firework going off; others are very slow like the forming of coal. The majority of reactions rates lie between these 2 examples.
unit_1_rates_of_reaction_notes.docx