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Chemical Reactions

Chemical Reactions. Chapter 20. Physical Changes. A physical change is a change that affects only the physical properties of a substance. These properties include: Size Shape State (liquid vs solid). Chemical Changes.

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Chemical Reactions

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  1. Chemical Reactions Chapter 20

  2. Physical Changes • A physical change is a change that affects only the physical properties of a substance. • These properties include: • Size • Shape • State (liquid vs solid)

  3. Chemical Changes A chemical change is a change in substance that involves breaking and reforming bonds to make one or more different substances.

  4. Chemical Changes Four indicators of chemical change are: 1. Formation of a new gas 2. Formation of a new solid 3. Release of energy (heat or light) 4. Color Change

  5. Chemical Reactions • In chemical reactions, you start with reactants that are combined to make products. -The reactants are the starting substances -The products are the new substances which result from the chemical reaction

  6. Chemical Reactions Reactants Products

  7. Chemical Reactions

  8. Chemical Reactions • In this reaction, methane (natural gas) is burnedor combusted. • Some energy is added to get the reaction started.

  9. Reaction Symbols • The small symbols in the parentheses (s, l, g, aq) next to each chemical formula indicate the phase of each substance in the reaction.

  10. Reaction Symbols • An arrow is always included between reactants and products. • It means “to produce” or “to yield.” to produce Reactants Products “Methane combines with oxygen gas to produce carbon dioxide gas and water vapor.”

  11. Conservation of Mass (atoms) • Antoine Laurent Lavoisier, established an important principal based on his experiments with chemical reactions. • He stated that the total mass of the products of a reaction is equal to the total mass of the reactants. • The law of conservation of mass holds true for even a burning mass of wood.

  12. Conservation of Mass (atoms) • The combined mass of the burning wood and oxygen is converted into carbon dioxide and water.

  13. Conservation of Mass (atoms) • Lavoisier showed that a closed system must be used when studying chemical reactions. • When chemicals are reacted in a closed container, you can show that the mass before and after the reaction is the same.

  14. Balancing Reactions • The law conservation of mass is applied by balancing the number and type of atoms on either side of the equation.

  15. Balancing Reactions • Counting atoms is necessary to balance an equation. How many carbon atoms? How many hydrogen atoms? How many oxygen atoms?

  16. Balancing Reactions • A balanced chemical equation has the same number of each type of atom on the product side and the reactant side. • To balance the equation, we add another water molecule to the product side and add another oxygen molecule to the reactant side.

  17. Balancing Reactions Steps for Balancing: • If not provided, write the word form of the equation. • If not provided, write the chemical equation from the word form. • Count the number of each type of atom on both sides. • Add coefficients to balance the equation.

  18. Balancing Reactions Step 1: Calcium carbonate reacts with hydrochloric acid to produce calcium chloride, carbon dioxide and water. Step 2:

  19. Balancing Reactions Step 3: Step 4:

  20. Types ofReactions There are 6 types of chemical reactions. 1. Addition/Synthesis Reactions 2. Decomposition Reactions 3. Single Displacement Reactions 4. Double Displacement Reactions 5. Precipitation Reactions 6. Combustion Reactions

  21. Addition/Synthesis Reactions • In an addition reaction, two or more substances combine to form a new compound.

  22. Addition/Synthesis Reactions A+B----->AB Fe (s)+O2 (g)----->Fe2O3(s) Remember to balance! Fe+O2----->Fe2O3 4 3 2

  23. DecompositionReactions • A chemical reaction in which a single compound is broken down to produce two or more smaller compounds is called a decomposition reaction.

  24. DecompositionReactions AB-energy-> A+B 2 H2O (l) -electricity-> 2 H2(g) + O2 (g)

  25. Single Displacement Reactions • In a single-displacement reaction, one element replaces a similar element in a compound.

  26. Double Displacement Reactions • In a double-displacement reaction, ions from two compounds in solution exchange places to produce two new compounds. • One of the compounds formed is usually a precipitate that settles out of the solution, a gas that bubbles out of the solution, or a molecular compound such as water.

  27. Double Displacement Reactions AB+CD--->AC+BD Pb(NO3)2+ KI--->PbI2+KNO3 2 2

  28. Precipitation Reactions • A precipitate is a new solid product that comes out of solution in a chemical reaction. • The formation of a cloudy precipitate is evidence that a double-displacement reaction has occurred.

  29. Precipitation Reactions • The limewater test for carbon dioxide is a precipitation reaction.

  30. CombustionReactions • A combustion reaction, also called burning, occurs when a substance such as wood, natural gas, or propane combines with oxygen and releases a large amount of energy in the form of light and heat.

  31. CombustionReactions CxHy+O2---> CO2+H2O+energy C6H12O6+O2---> CO2+H2O 6 6 6 +energy

  32. Types ofReactions

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