Chapter 7 Chemical Reactions

Vocab Reactants Products Chemical Equations Coefficients

Chemical Equations Law of Conservation of Mass - Mass cannot be created or destroyed. The mass of the reactants must equal the mass of the products in a chemical reaction.

Balancing Chemical Equations In other words, The total number of each type of atom must be the same on both sides of the equation.

Do’s and Don’ts Do: Write the equation with the correct symbols and formulas Count the number of atoms on each side. Use coefficients to change the totals. Check your work by recounting.

Do’s and Don’ts Don’t: Change subscripts! Change the chemical formulas or symbols. Add coefficients in the middle of a formula.

Balancing Equations H2 +O2 H20 What happened to the other O? It can’t just disappear. Mass must be conserved.

Balancing Equations C + H2 CH4 2

Some to try. Zn + HCl ---> ZnCl2 + H2 KClO3 ---> KCl + O2 S8 + F2 ---> SF6 Fe + O2 ---> Fe2O3 C2H6 + O2 ---> CO2 + H2

Types of Chemical Reactions Synthesis Decomposition Single Replacement Double Replacement Oxidation/Reduction Combustion

Synthesis Combining two or more simple substances to make a more complex one. A + B AB 2Na +Cl2 2NaCl

Decomposition A complex substance breaks down into two or more simpler substances AB A + B 2 H2O 2H2 + O2

Single Replacement An uncombined element replaces an element that is part of a compound. A + BX AX + B Zn + 2HCl ZnCl2 + H2

Double Replacement Atoms in different compounds trade places AX + BY AY + BX CaCO3 + H2SO4 CaSO4 + H2CO3

Combustion

Energy of Reactions Exothermic – gives off energy Endothermic – absorbs energy. Activation Energy – energy required to start a reaction.

Reaction Rates Increasing Temperature increases reaction rate Surface Area – increasing the surface area increases the rate of reaction. Concentration – amount of reactants in a given volume. Stirring increases reaction rate Catalyst – speeds up a reaction but does not change during the reaction