Chemistry – Feb 15, 2018 Agenda ID chemical reactions P3 Challenge – Nomenclature quiz 3 May use own periodic table No other resources Objective – Balancing Reactions Assignment: Balancing Reactions Worksheet Agenda ID chemical reactions Chemical equation notation Balance equations Write equations from word descriptions Break extra credit assignment

Evidence of a possible chemical reaction (review) Color change (ex: rust formation) Formation of a solid (ex: hard water deposits) Formation of a gas (ex: Alka Seltzer) Emission of light (ex: fireworks) Spontaneous exchange of heat (heats up or cools down) (ex: hot/cold packs) These observations usually indicate a chemical change Phase changes also involve the formation of a solid or a gas, usually only due to heat addition/subtraction, not mixing another substance

Chemical Equations Chemical reactions are represented symbolically using chemical equations Ex: 2 C2H6 (g) + 7 O2 (g)  4 CO2 (g) + 6 H2O (g) The substances mixed together are called reactants. Their chemical formulas are listed with a + sign between them. Then an arrow represents the process of reacting. Any additional information about the reaction process may be written above or below the arrow. (Heat, light, catalyst…) The substances produced from the reaction are called products. Their formulas are listed with a + sign between them. Often, the state of each substance is stated in parentheses. (s, l, g, aq) Large numbers in front of each formula are called coefficients and are necessary to balance the equation.

Balancing Chemical Equations Because of the law of conservation of mass, the same number and types of atoms must be present on both sides of a chemical equation. Balance an equation by adding coefficients in front of chemical formulas as needed. DO NOT CHANGE FORMULA SUBSCRIPTS! (Verify all formulas are correct before balancing.)

Balancing Chemical Equations How to balance: 1. Make an inventory of the number and type of each type of element on each side of the equation. 2. Balance one element. Update the inventory. 3. Repeat for each element until all elements are balanced. 4. Verify each type of atom is balanced.

Some strategies and hints Avoid balancing an element that occurs in multiple compounds on one side until later. These elements often balance when other elements balance. Balance a free element last. When there is not a simple multiple of the numbers, try swapping numbers. When balancing a last diatomic element that needs an odd number of atom, double all other coefficients and then balance the diatomic.

Balancing equations Examples _____Li2O + _____H2O _____LiOH _____NH3 + _____NO _____ N2 + _____H2O _____FeCl3 + _____NH4OH  _____Fe(OH)3 +_____NH4Cl _____C5H12 + _____O2  _____CO2 + _____H2O

Balancing practice _____ H2 + _____ O2  _____ H2O _____ Fe + _____ Cl2  _____ FeCl3 _____ Cu + _____ AgNO3  _____ Cu(NO3)2 + _____ Ag _____ Zn + _____ HCl  _____ ZnCl2 + _____ H2 _____ Pb(NO3)2 + _____ AlCl3  _____ PbCl2 + _____ Al (NO3)3 _____ LiClO3  _____ LiCl + _____ O2 _____ Mg(OH)2 + _____ HCl  _____ MgCl2 + _____ H2O

Exit Slip - Homework _____Fe2O3 + _____C  _____CO + _____Fe Exit Slip: Balance the following chemical equation: _____Fe2O3 + _____C  _____CO + _____Fe What’s Due? (Pending assignments to complete.) Complete the Balancing Reactions Worksheet, ignore “typing” directions on pg 2. What’s Next? (How to prepare for the next day Read p263-285