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Section 4.1 CHEMICAL REACTIONS

Understand the process of chemical reactions and the factors that influence the rate of reaction. Learn about reactants, products, indicators of chemical reactions, and the laws governing conservation of mass. Discover how catalysts, concentration, temperature, and surface area can affect reaction rates.

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Section 4.1 CHEMICAL REACTIONS

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  1. Section 4.1CHEMICAL REACTIONS

  2. A chemical reaction occurs when 2 or more substances combine to form a new substance. • Reactants – materials that are combined to start a reaction • Products – new materials produced by the reaction

  3. A chemical reaction can be written as a word equation, with reactants on the left and products on the right. • Label the reactants and products in the following word equation: wood + oxygen ---- carbon dioxide + water + energy

  4. A chemical reaction can be written as a word equation, with reactants on the left and products on the right. • Label the reactants and products in the following word equation: wood + oxygen ---- carbon dioxide + water + energy REACTANTS Left side PRODUCTS Right side

  5. Remember:Indicators of Chemical Reactions are: • color change • Change in odour • formation of a solid (precipitate) or a gas • release or absorption of energy.

  6. Chemical Reactions Involving Energy • Exothermicreactions release energy to the surroundings. • Give 1 example:

  7. Endothermic reactions absorb energy from their surroundings. • Give 1 example:

  8. Chemical Reactions Involving Oxygen • A combustionreaction occurs when oxygen reacts with a chemical to produce a new substance and a release of energy.

  9. Corrosionoccurs when oxygen in the air reacts with a metal, such as the rusting of iron.

  10. Cellular respiration takes place in body cells. It is the reaction of oxygen with glucose from food to produce water, carbon dioxide and energy.

  11. Write a word equation and then a chemical equation for the following reactions: • When hydrogen peroxide (H2O2) is left out in the sun it decomposes into water and oxygen gas.

  12. Write a word equation and then a chemical equation for the following reactions: • When hydrogen peroxide (H2O2) is left out in the sun it decomposes into water and oxygen gas. Hydrogen peroxide + sunlight water + oxygen H2O2 + sunlight H2O + O2

  13. 2. Iron left exposed to the atmosphere rusts.

  14. 2. Iron left exposed to the atmosphere rusts. iron + oxygen iron oxide Fe + O2 FeO or Fe + O2 Fe2O3

  15. 3. Sodium and bromine react explosively to produce sodium bromide.

  16. 3. Sodium and bromine react explosively to produce sodium bromide. sodium + bromine sodium bromide + Energy Na + Br2 NaBr + Energy

  17. Section 4.2 Conservation of Mass • The Law of Conservation of Mass: • In any chemical reaction, the total mass of the reactants is equal to the total mass of the products. • matter is neither created nor destroyed during chemical reactions, though it may change in appearance.

  18. Sometimes it may appear as though this law is not upheld; when Alka-Seltzer is added to water fizzing occurs as the reaction proceeds. • The final mass of the products is less then the initial mass of the reactants. Why is this? What is an open system?

  19. The law is proven in a closed system, where additional materials are not able to enter or leave during a chemical reaction. • If the beaker were capped, the gas would be forced to stay in the beaker. • The final mass would equal the initial mass.

  20. Reactants Products

  21. Section 4.3 Factors Affecting the Rate of Reaction Catalysts • A catalyst helps a reaction proceed more quickly. • It is not altered during the reaction, so it is NOT a reactant. • In your intestine, many catalysts, called enzymes, are working to speed the rate of breaking down food.

  22. The shape of the enzyme molecule helps the reactant molecule break down. • Note that the enzyme is not changed by the reaction.

  23. Concentration • With more reactants, a reaction proceeds more quickly. There are more atoms of each reactant available to react.

  24. Temperature • An increase in temperature also speeds the rate of reaction. This is because with more heat, atoms of each reactant move faster and collide with each other more often. Products then form more quickly.

  25. Surface Area • When the surface area of a reactant is increased, reaction rate speeds up. This occurs because more of the reactant is available to react.

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