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Don’t Over-react!!!!!. Chemical reaction . when two or more substances combine to form new substances. Reactants – start the reaction (usually on the left side of the arrow ) Products – the new material that is produced (usually the right side of the arrow). Evidence:. Colour change

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Chemical reaction
Chemical reaction

  • when two or more substances combine to form new substances.

  • Reactants – start the reaction (usually on the left side of the arrow)

  • Products – the new material that is produced (usually the right side of the arrow)


Evidence
Evidence:

  • Colour change

  • Odour

  • Gas bubbles

  • Solid precipitate

  • Heat given off/absorbed


Endothermic vs exothermic
Endothermic vs. Exothermic

  • Think of breathing – exhale – breathe out, inhale – breathe in

  • Endothermic – energy taken in from the surroundings, the surrounding environment gets colder

  • Exothermic – energy is given off – surrounding environment gets warmer


Common chemical changes
Common Chemical Changes

  • Oxygen is often involved with chemical changes

  • 1. Combustion – burning requires oxygen (man’s first chemical reaction!!)

  • 2. Corrosion – oxygen in the air reacts with a metal (e.g. rusting – iron + oxygen iron oxide)

  • 3. Cellular Respiration – takes place in the cells of your body. Food + oxygen energy, water, and carbon dioxide. (Hint: What is the opposite of cellular respiration??)


Don t break the laws
Don’t Break The Laws!!!!

  • How chemical reactions follow the different laws

  • Law of Conservation of Mass – the total mass of the products is always the same as the total mass of the reactants (even if you can’t see it anymore). This requires a closed system.

  • Law of Definite Composition – every reactant and product in a chemical reaction exist in definite proportions. There cannot be partial pieces of elements.

  • Law of Multiple Proportions – in a chemical reaction, when elements are rearranged to make new compounds, the proportions of each element on the reactant side must equal its proportion on the product side.

    This is known as balancing equations


Factors affecting the rate of reaction
Factors affecting the rate of reaction

  • Presence of a catalyst – e.g. enzymes

  • Concentration of reactants

  • Temperature of reactants

  • Surface area of reactants


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