8.1 What is a chemical reaction?What is a chemical reaction? I. Chemical Reaction: A. Chemical change, where one or more substances changes into one or more new substances. B. Reactants- substances going into a reaction. C. Products- substances formed after a reaction has occurred.

8.1 Types of Evidence (video)(video) AA. Heat and Light Exothermic reactions you will see this. BB. Production of Gas Gas Bubbles are an indication. CC. Formation of a Precipitate A solid appears after two solutions are mixed. DD. Color change Colors of the solution.

8.1 Collisions V. Collisions A. Collisions cause bonds to break if there is enough energy. B. Increasing temperature increases collisions. C. Shaking, stirring, or increasing surface area increases collisions. Video: how to get a date!

8.1 Exothermic reactions B. Exothermic- when more energy is released in bond formation than was absorbed to break the bonds. 1. May require heat to start if at room temperature. 2. Energy is released in the form of heat and light. 3. Most reactions in nature are exothermic. Example of word equation: Hydrogen + Oxygen  Water + Energy

8.1 Endothermic reactions C. Endothermic- when more energy is put into a reaction than is released when the reaction is over. Energy is absorbed from surroundings! Feels COLD to the touch (energy leaving hands) Example of word equation: Water + Energy  Hydrogen + Oxygen

8.1 Conservation of Mass A. Law of conservation of mass- mass is never created or destroyed. B. When chemical changes occur, the bonding patterns are rearranged among the atoms involved. C. Whatever atoms are found in the reactants, must be found in the products.

Symbols used in Chemical Equations  Yields   Reversible  Solid state or precipitate (s)  Liquid state (l)  Gaseous State (g)  Dissolved in water (aqueous solution) (aq)  Reactants are heated Pressure (atms) atm  Temperature of reaction C  Catalysts added MnO 2

Symbols used in Chemical Equations  Solid calcium reacts with solid sulfur to produce solid calcium sulfide. 8 Ca (s) + S 8 (s)  8CaS (s)  NaCl (aq) + AgNO 3 (aq)  NaNO 3 (aq) + AgCl (s ) Aqueous solutions of sodium chloride and silver nitrate react to produce aqueous sodium nitrate and a precipitate of silver chloride.

Significance of Chemical Equations  1. The coefficients indicate relative amounts of products and reactants (ratios).  The relative masses of the reactants and products can be determined by using the coefficients and the molar mass. H 2 + Cl 2  2HCl  1 mol H 2 x 2.02 g/ mol = 2.02 g H 2  1 mol Cl 2 x g/ mol = g Cl 2  2 mol HCl x g/mol = g HCl  Conservation of mass!!!!!

Balancing Chemical Equations  You can only change the coefficients! Never the subscripts!  You can only add coefficients in front of the compound! Never in the middle or at the end  You cannot change the subscript behind ( ).  The atoms on the left must equal the atoms on the right Therefore, the mass on the left = mass on the right.

Practice Balancing Equations  ___ H 2 + ___ O 2  ____ H 2 O 4 H 2 O4 O 2 H  __SrBr 2 + __(NH 4 ) 2 CO 3 → __SrCO 3 + __NH 4 Br Balance this by keeping the polyatomic ions together. (groups of (NH 4 ) 2 2 2

Tips for balancing equations  Look to see if the equation is already balanced.  Start with Carbons.  Leave the Hydrogen and Oxygen last.  Balance polyatomic ions as a group.

Websites for practice  ng-chemical-equations ng-chemical-equations  /au_sch_derry_ibcsl_1/int/balancingEquations /BalancingEquations.html /au_sch_derry_ibcsl_1/int/balancingEquations /BalancingEquations.html