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Describing Chemical Change. Signs of a Chemical Change . Look for evidence of something new having been made. Common signs include: Color change Temperature change Formation of a solid Formation of a gas. Chemical Reactions. Write chemical reactions/equations to describe chemical change.
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Signs of a Chemical Change • Look for evidence of something new having been made. • Common signs include: • Color change • Temperature change • Formation of a solid • Formation of a gas
Chemical Reactions • Write chemical reactions/equations to describe chemical change. • A correctly written chemical reaction will • Obey the law of conservation of matter • Show the chemical formula and state of each reactant and product
Correctly written reaction Mg(s) + 2 HCl(aq) MgCl2 (aq) + H2 (g)
Writing Chemical Reactions • Write chemical formula for each reactant and product – use naming rules to do so • Often already done for you…..except on a take home exam. • Write a symbol after each reactant and product to indicate its state. • You will be given enough information to do this.
Writing Chemical Reactions • Balance the reaction by adding coefficients in front of any reactant and/or product. • The goal is to have the same number of each type of atom on the two side of the equation. • If you have 2 Cl atoms on the product side of the equation you must also have 2 Cl atoms on the reactant side.
Writing Chemical Reactions • Balance the reaction by adding coefficients in front of any reactant and/or product. • You may NOT change the chemical formula of the reactants or products to balance the reaction.