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Chemical Reactions and Chemical Equations. Quick Review Physical Change A physical change in a substance doesn't change what the substance is. Example:

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Presentation on theme: "Chemical Reactions and Chemical Equations. Quick Review Physical Change A physical change in a substance doesn't change what the substance is. Example:"— Presentation transcript:

1 Chemical Reactions and Chemical Equations

2 Quick Review Physical Change A physical change in a substance doesn't change what the substance is. Example: tearing paper, it is still paper

3 Chemical Change In a chemical change a new substance is formed and energy is either given off or absorbed. Example: burning paper The paper is changed into carbon, water, and heat is given off.

4 Chemical Change When substances undergo a chemical change, the new substances will have different properties. For example: Burning wood in a campfire.

5 Evidence of a Chemical Change Color change Light is released A solid (precipitate) is produced An odor is evident Temperature changes A gas is given off Sound is produced

6 Law of Conservation of Matter Remember that? Matter is NEVER created or destroyed in a chemical change. The particles are just rearranged to form new substances. The same number of particles that existed before the change exist after the change! It’s the law!!!!!

7 Chemical Equations When writing chemical equations, you MUST follow the law of Conservation of Mass. There must be the same # and kind of atoms on each side of the arrow. This is referred to as balancing an equation

8 Let’s Try Some H 2 + O 2 H 2 O gas gas liquid Balanced? Let’s balance it: 2H 2 + O 2 2H 2 O Na + Cl NaCl soft, reactive metal poisonous gas white solid Balanced? That is why you see large numbers in front of elements and compounds, to balance the # of atoms on each side of the arrow.

9 Types of Chemical Equations Synthesis (A + B AB) Na + Cl NaCl Decomposition (AB A + B 2H 2 O 2 2H 2 O + O 2

10 Types of Chemical Reactions Single Replacement (AB + C AC + B) Mg + HCl MgCl 2 + H 2 (How do I balance this?) Double Replacement (AB + CD AD + BC) Na 2 CO 3 + CaCl 2 NaCl + CaCO 3 (How do I balance this?)

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