Chemical Reactions

Chemical Change New substance is formed Compare original substance Reactant with the new substance Product Reactant + Reactant  Products

Reactants Products Can be written as Carbon plus oxygen gas yields carbon dioxide

You cant get something from nothing The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. What you start with you must end up with No POOF! Its gone type of stuff.

types of chemical reactions synthesis reactions decomposition reactions single-replacement reactions double-replacement reactions combustion reactions.

Synthesis reactions A + B  AB 2 or more reactants 1 product Think Dating! Example from this year: H2+ O2 H2O

Decomposition One Reactant Two or more products AB A + B Think Breakup Example from this year H2O  H2 + O2 H2O2  H2O + O2

Single Replacement A + BC AC + B An element will replace another element in a compound The old “switcheroo” Single girl goes in and takes guy from another girl Example from this year Zn + HCl ZnCl2 + H2

Double Replacement AB + CD AD + CB Compounds recombine into different compounds Think two dates where they swap partners

Combustion Oxygen burning with a hydrocarbon produces water and carbon dioxide O2 + CHx  CO2 + H2O

Balancing Reactions In order to show that mass is conserved during a reaction, a chemical equation must be balanced.

Balancing rules balance a chemical equation by changing the coefficients. When you change a coefficient, you change the amount of that reactant or product represented in the chemical equation. As you balance equations, you should never change the subscripts in a formula. Changing the formula changes the identity of that reactant or product.

Follow this series of questions Follow this series of questions. When you can answer "yes" to a question, then stop! 1)  Does your reaction have oxygen as one of its reactants and carbon dioxide and water as products? If yes, then it's a combustion reaction 2)  Does your reaction have two (or more) chemicals combining to form one chemical product? If yes, then it's a synthesis reaction 3)  Does your reaction have one large molecule falling apart to make several small ones? If yes, then it's a decomposition reaction 4)  Does your reaction have reactants that contain only one element and products that contain only one element? If yes, then it's a single displacement reaction 5)  If you haven't answered "yes" to any of the questions above, then you've got a double displacement reaction

Exothermic reaction a chemical reaction that releases energy to its surroundings Released as heat and light

Endothermic reaction a chemical reaction that absorbs energy from its surroundings Add heat to get the reaction to occur

Reaction Rates the rate at which reactants change into products over time

Factors that affect Reaction Rates Temperature surface area Concentration Stirring catalysts.