Chemistry 141 Lecture 7 Wednesday, September 20, 2017

Your turn For each pair below: Predict the formula of the compound they form Write the name of the compound Ca and NO3- Cr(III) and SO42- NH4+ and S H and PO43- 2 N’s and 5 O’s Ca(NO3)2 calcium nitrate Cr2(SO4)3 chromium(III) sulfate (NH4)2S ammonium sulfide H3PO4 phosphoric acid N2O5 dinitrogen pentoxide

Objectives for today Write and balance chemical equations Identify types of reactions (combination, decomposition, and combustion) Determine formula and molecular weights and percent composition from compound formulas Understand and use the mole concept Determine empirical formulas from mass data

The Law of Conservation of Mass Matter cannot be created or destroyed (Lavoisier, “The father of modern chemistry”, 1789) “…an equal amount of matter exists both before and after the experiment. Upon this principle, the whole art of performing chemical experiments depends.”

Your turn How many atoms of Mg, O, and H are represented by the notation 3 Mg(OH)2? 1 Mg, 2 O, and 2 H 2 Mg, 2 O, and 2 H 6 Mg, 6 O, and 6 H 3 Mg, 6 O, and 6 H Answer: d

CH4(g) + 2O2(g) CO2(g) + 2H2O(g) States of matter CH4(g) + 2O2(g) CO2(g) + 2H2O(g) The states of the reactants and products are written in parentheses to the right of each compound. (g) = gas (l) = liquid (s) = solid; (aq) = in aqueous solution

Balance the following equation: AlCl3 (s) + Ca3N2 (s)  AlN (s) + CaCl2 (s) What is the coefficient of CaCl2 in the balanced equation?

Three Types of Reactions Combination reactions Decomposition reactions Combustion reactions

Combination Reactions In combination reactions two or more substances react to form one product. 2 Mg(s) + O2(g) 2 MgO(s)

Decomposition Reactions In a decomposition reaction one substance breaks down into two or more substances. 2 NaN3(s) 2 Na(s) + 3 N2(g)

Combustion Reactions CH4(g) + 2 O2(g) CO2(g) + 2 H2O(g) Combustion reactions most often involve oxygen in air as a reactant and can produce a flame. CH4(g) + 2 O2(g) CO2(g) + 2 H2O(g)

The formula weight of Na3PO4 is _______ grams per mole. 70 164 265 116 Answer: b

The percentage by mass of phosphorus in Na3PO4 is 44.0. 11.7. 26.7. 18.9. Answer: d

What number would you use to convert grams of CH4 to moles of CH4? Avogadro’s number, 6.02 × 1023 particles/mol Inverse of molar mass of CH4, 1 mol CH4/16.0 g CH4 Molar mass of CH4, 16.0 g CH4/1 mol CH4 Formula weight of CH4, 16.0 amu Answer: c