Unit 1.1 - Chemical Reactions

Change
1. Physical
  1. No new substances are formed. Examples boiling, melting, freezing, condensing, dissolving
2. Chemical
  1. Atoms are arranged to form new substances. Examples: permanent colour change, the production of a new solid, liquid or gas, or when energy is produced or absorbed energy is produced or absorbed
  2. A permanent change in colour—toast turning brown and leaves changing their colour in autumn are signs that a chemical reaction has taken place.
  3. A new solid (precipitate) forms
  4. Energy being absorbed or produced—this change will be accompanied by a drop in temperature or the release of heat and light.
Symbols & Formulae
1. Element Symbols
  1. Basic building blocks. 118 basic types of atom: 92 naturally occurring & 26 are not
2. Chemical Formulae
  1. Molecules
    1. What type & how many atoms. Eg H2O, C6H12O6
  2. Lattices
    1. What type & proportion of atoms. Eg NaCl
    2. Covalent Bonding: Only occur between non-metal atoms
    3. Ionic bonding almost always involves metals combined with non-metals
Chemical Equations
1. Can be written as a word equation or a formula equation
2. Substances present at the start are reactants and the new substances formed are known as the products
Balanced chemical equations
1. How many reactant molecules needed and how many product molecules are produced
  1. The Conservation of Mass = Atoms cannot appear from nowhere nor disappear into thin air.
2. State of reactants and products
Controlling Reaction Rates
1. Changing the Temperature: Faster - Increase temperature
2. Concentration: The concentration of reactants or products determines the rate of reaction. Faster - Increase reactants or decrease products
3. Changing surface area: Faster - More reactant surface area, more molecules react
4. Catalysts: Help the reactant molecules to form the products, but are not changed or used up in the reaction. Eg UV used to harden dental fillings
5. Enzymes: Special types of catalysts, like a pair of scissors. Do not combine with other atoms or molecules; Eg Digestive Enzymes

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Unit 1.1 - Chemical Reactions

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