Chemical Reactions 10 10 13 Chemical change reacting substances form new substances with different compositions and properties Tarnish on silver silver sulfide Hydrogen sulfide and silver Evidence of chemical change Color Formation of a gas Formation of a solid Heat produced or heat absorbed Chemical Equation Recipes know what you start with and what you end with Start and final listed Chemical equation is an expression in which symbols and formulas are used to represent a chemical reaction Reactant Substance that undergoes change in chemical reaction and is written on the left side of the reaction arrow Product Substance that is formed in a chemical reaction and is written on the right side of the reaction arrow in a chemical equation o No coefficient one o Symbols Used in chemical equations show ths states of the reactants and the states of the products o S solid o L liquid o G gas or vapor o Aq aqueous Most will be aqueus precipitation reaction If you accidently mix two together that precipitate not good Liquids are pure aqueous solutions are mixtures Chemical Changes occur through chemical reactions Chemical reaction old bonds are broken and new bonds are formed The atoms in the reactants are rearranged to form one or more different substances Old bonds break New bonds re form You cannot add or subtract any from that reaction o Reactants must be in products Must be balanced Law of conservation of mass matter cannot be created or destroyed in chemical reaction Bonds between atoms in reactants are rearranged to form new compounds None of the atoms disappear no new are formed Balanced chemical reaction Atoms are not lost or gained Atoms in reactants to number in products Chemical equations are balanced In balanced reaction atoms are not lost or gained Balanced chemical equations AL S Al2 S3 Add coefficents in front of formulas 2Al 3S subscrpits cannot change Steps 1 write unbalanced equation using correct formulas and products 2 add appropriate coefficients to balance the numbers of atoms in each element A polyatomic ion appearing on both sides of an equation can be treated as a single unit 3 Check the equation to make sure the numbers and kinds of atoms on bth sides are the same a Count up each to make sure 4 make sure the coefficients are reduced to their lowest WHOLE number ratio Only with coefficients Types of chemical reactions Precipitation reaction insoluble solid forming Acid base neutralization processes in which H ions from an acid react with OH ions from a base to yield water Oxidation reduction reactions are processes in which one or more electrons are transferred between reaction partners Precipitation reactions Two aqueous solutions mix Chemical reaction occurs solid forms Precipitate Insoluable solid o Lead nitrate and potassium iodide Solibility Low water solubility will form solids High water solubility will stay aqueous Solubility amount of compound that will dissolve in a given amount of solvent at a given temperature Typically soluable ions o If compound has an 1A cation o Halide Nitrate Acetate perchlorates sulfates SOME EXCEPTIONS JUST general rules 1A 7A and polyatomics Terminology Precipitation reaction occurs one or both products are not water soluable Product in this case is aqueous slide Formation of a solid Use the solubility rules to predict whether a solid is called a precipitate forms when two solutions of ionic compounds are mixed Solid drifts to bottom of the test tube Ionic equations Reactions involving ions it is more accurate to write the reaction as an ionic equation Where ions are explicitly shown Look at changes and how they effect ions individually Net ionic equations The actual reaction can be described more simply by writing a net ionic equation o Ions undergo change Net ionic equation Take aqueous and break them apart in the reactant side The net ionic equation confirms a precipitation reaction o Ag and Cl both aqueous change to solid o The rest in this equation are just spectator ions