Chemical Reactions Objectives: 1.Write a word equation 2.Write a skeletal equations 3.Describe the parts to a chemical reaction

All Chemical Reactions have 2 Parts Reactants—what you start with Products—what you end with Reactants turn into products Reactants  Products

Law of Conservation of Mass Atoms aren’t created nor destroyed, just rearranged Can be expressed in a few ways: Sentence: – Copper reacts with chlorine to form copper(II) chloride Word equation – Copper + chlorine  copper(II) chloride Skeletal – Cu + Cl  CuCl

Symbols Arrow (  ) separates reactants from products (points to products) – Read as “reacts to form” or “yields” +-- “and” (s) after formula—solid (g) after formula= gas (l) after formula=liquid (aq)—dissolved in water—aqueous solution Double arrow—reversible reaction

More Symbols or with “heat” over arrow—heat is used in the reaction Arrow with “catalyst” or “enzyme” above it means a catalyst or enzyme was used. Sometimes they will use the actual enzyme.

Catalyst Substance that speeds up a reaction, without being changed or used up by the reaction. Enzymes are biological catalysts in your body

Skeletal Equations Uses formulas and symbols to describe a reaction – Does not indicate how many, they are NOT balanced

Writing Skeletal Equations Solid Iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (III) chloride and hydrogen sulfide gas.

Reverse it! Fe (s) + O 2(g)  Fe 2 O 3(s) Cu (s) + AgNO 2(aq)  Ag (s) + Cu(NO 3 ) 2(aq) NO 2(g)  N 2(g) + O 2(g)

Balancing Chemical Equations Atoms can’t be created or destroyed – All the atoms we start with we must end up with A balanced equation has the same number of each element on both sides of the equation

Rules Assemble the correct formulas for all the reactants and products Count the number of atoms of each type appearing on both sides Balance the elements one at a time by adding coefficients (number in the front). Balance Hydrogen and Oxygen last! Double check

What NOT to do Never change a subscript to balance an equation Never put a coefficient in the middle of a formula

Example

Practice (balance)

Practice (balance and give word equation)

Give the chemical equation and then balance Zinc and lead (II) nitrate react to form zinc nitrate and lead. Aluminum bromide and chlorine gas react to form aluminum chloride and bromine gas Sodium phosphate and calcium chloride react to form calcium phosphate and sodium chloride