Chemistry – Jan 23, 2017 P3 Challenge – Today’s Objective – Write the chemical formula for calcium hydroxide hydrochloric acid calcium chloride Today’s Objective – Balancing Reactions

Chemistry – Jan 23, 2017 Objective – Balancing Reactions Assignment: Balancing Reactions Worksheet Agenda ID chemical reactions Chemical equation notation Balance equations Write equations from word descriptions 5 types of reactions

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 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!) 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 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

Word Equations When solid sodium metal reacts with liquid water, an aqueous solution of sodium hydroxide and hydrogen gas are formed. When aqueous calcium chloride and aqueous sodium sulfate are mixed a white solid of calcium sulfate forms in an aqueous solution of sodium chloride. The reaction of aqueous silver nitrate and aqueous sodium chromate that forms solid silver chromate and aqueous sodium nitrate.

Types of reactions Synthesis (Combination) Decomposition A + B  AB Two elements react to form a compound Decomposition AB  A + B A compound is separated into its elements Single Replacement A + BC  AC + B One element takes the place of another in a compound. Double Replacement AB + CD  AD + CB Ionic partners switch

Combustion The reaction with oxygen is so common that it is often given its own classification: combustion. The products of a combustion are always the oxides of the elements in the other reactant. If there is a choice of metal ion, you will be told what ion charge to use. Ex: Fe + O2  Fe2O3 Ex: CH4 + O2  CO2 + H2O Ex: Li + O2  Li2O Classify each of the reactions from previous slides.

Reaction Types Overview Reactants Reaction Type Products Two elements Synthesis (S) Compound of the two elements A single compound Decomposition (D) Component elements (or simpler substances) An element and a compound Single replacement (SR) Different element and compound Two compounds Double replacement (DR) Two different compounds Reaction with oxygen Combustion (C) Oxides of each element in other reactant

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