University:
Montgomery College
Course:
CHEM 131: Principles of Chemistry I
Academic year:

2020
Views:

377

Pages:

2
Author:

Annalise Walters

Writing Balanced Chemical Equations Writing Formulas for Ionic Compounds 1. Write the symbol for the metal cation and its charge Al3+ column 3A 2. Write the symbol for the nonmetal anion and its charge O2− column 6A 3. Charge (without sign) becomes subscript for other ion Al3+ O2Al2O3 4. Reduce subscripts to smallest whole number ratio Al = (2)·(+3) = +6 O = (3)·(−2) = −6 5. Check that the sum of the charges of the cations cancels the sum of the anions Balancing Double Displacement Reactions (AB + CD AD + CB) Na2S + HgCl2 Na2S: Na+ and S2- 1. Identify the cations and anions in each compound HgCl2: Hg2+ and Cl¯ 2. Pair up each cation with the anion from the OTHER compound Na+ pairs with Cl¯ Hg2+ pairs with S2- 3. Write two new (CORRECT!!) formulas using the pairs from step two NaCl 4. Adjust coefficients to ensure mass conservation 5. Check Hg2S2 2  Na  1 x 2 Na2S + HgCl2 2 NaCl + HgS Na2S + HgCl2 Balancing Combustion Reactions (organic compounds + O2 1. Write a skeletal equation 2. Balance atoms in complex substances first HgS 2 NaCl + HgS(s) CO2+ H2O) C4H10(l) + O2(g)  CO2(g) + H2O(g) 4C1x4 C4H10(l) + O2(g)  4 CO2(g) + H2O(g) 10  H  2 x 5 C4H10(l) + O2(g)  4 CO2(g) + 5 H2O(g) 3. Balance free elements by adjusting coefficient in front of free element 13/2 x 2  O  13 C4H10(l) + 13/2 O2(g)  4 CO2(g) + 5 H2O(g) 4. If fractional coefficients, multiply thru by denominator {C4H10(l) + 13/2 O2(g)  4 CO2(g) + 5 H2O(g)}x 2 2 C4H10(l) + 13 O2(g)  8 CO2(g) + 10 H2O(g) 5. Check 8  C  8; 20  H  20; 26  O  26 Practice Problems 1. Write the empirical formulas for the compounds formed by the following ions: a) Al3+ and O2- ions b) Mg2+ and NO3- ions c) Na+ and PO43- ions d) Fe3+ and CO322. Balance each chemical equation: a) H2 (g) + Cl2 (g) HCl (g) b) Cu2O (s) + C (s) Cu (s) + CO (g) c) C2H4 (g) + O2 (g) CO2 (g) + H2O (l) d) C8H8 (l) + O2 (g) CO2 (g) + H2O (l) e) CH3OH (l) + O2 (g) CO2 (g) + H2O (l) f) K2CO3 (aq) + NiCl2 (aq) NiCO3 (s) + KCl (aq) g) NaCl (aq) + AgNO3 (aq) h) Ca(NO3)2 (aq) + Na2SO4 (aq) i) NaOH (aq) + FeCl3 (aq) References: Tro, Chemistry: A Molecular Approach 2nd ed., Pearson Brown/LeMay/Bursten, Chemistry: The Central Science, 12th ed., Pearson i) 3 NaOH (aq) + FeCl3 (aq) 3 NaCl (aq) + Fe(OH)3 (s) h) Na(NO3)2 (aq) + Na2SO4 (aq) g) NaCl (aq) + AgNO3 (aq) CuSO4 (s) + 2 NaNO3 (aq) NaNO3 (aq) + AgCl (s) NiCO3 (s) + 2 KCl (aq) f) K2CO3 (aq) + NiCl2 (aq) 2 CO2 (g) + 4 H2O (l) e) 2 CH3OH (l) + 3 O2 (g) d) C8H8 (l) + 10 O2 (g) c) C2H4 (g) + 3 O2 (g) b) Cu2O (s) + C (s) 2. a) H2 (g) + Cl2 (g) 8 CO2 (g) + 4 H2O (l) 2 CO2 (g) + 2 Cu (s) + CO (g) 2 HCl (g) 1. a) Al2O3; b) Mg(NO3)2; c) Na3PO4; d) Fe2(CO3)3 Answers 2 H2O (l)