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Balancing Chemical Equations Part II. Balancing Chemical Reactions Follow these steps 1. Check for diatomic gases 2. Balance formulas of compounds 3.

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Presentation on theme: "Balancing Chemical Equations Part II. Balancing Chemical Reactions Follow these steps 1. Check for diatomic gases 2. Balance formulas of compounds 3."— Presentation transcript:

1 Balancing Chemical Equations Part II

2 Balancing Chemical Reactions Follow these steps 1. Check for diatomic gases 2. Balance formulas of compounds 3. Conservation of atoms 4. Add coefficients if needed 5. Conservation of Mass

3 A. Check For Diatomic Gases Diatomic Gases – molecules containing only two atoms. You must include the subscript “2” when the symbol is written by itself. Seven Diatomic Gases nitrogen, N 2 bromine, Br 2 oxygen, O 2 iodine, I 2 fluorine, F 2 hydrogen, H 2 chlorine, Cl 2 Name One Frozen Clam Broke In Hawaii

4 Diatomic Gases Example H 2(g) + O 2(g) → H 2 O (g) Hydrogen and oxygen are diatomic gases when written ALONE. You must include the subscript “ 2 ”. Note: The equation isn ’ t balanced.

5 Balancing A Decomposition Equation A.Check for diatomic gases H 2 O (ℓ) → H + O Diatomic gases: hydrogen & oxygen. Add a subscript “2” to each H 2 O (ℓ) → H 2(g) + O 2(g)

6 B. Check The Formulas of Compounds The compound in the equation is water. The formula is balanced. H 2 O (ℓ) → 2H 2(g) + O 2(g)

7 C. Same Elements on Both Sides H 2 O (ℓ) → H 2(g) + O 2(g) ReactantsProducts hydrogenhydrogen oxygenoxygen

8 D. Conservation of Atoms H 2 O (ℓ) → 2H 2(g) + O 2(g) 2 – H2 - H 1 – O2 – O Atoms aren’t conserved. Equation isn’t balanced.

9 E. Balanced Equation 2H 2 O (ℓ) → 2H 2(g) + O 2(g) The coefficients “2” are placed in front of water, and hydrogen. 4 – H 4 – H 2 – O 2 – O The equation is balanced.

10 F. Law of Conservation of Mass Mass of Reactants = Mass of Products 2H 2 O (ℓ) → 2H 2(g) + O 2(g) 2(18 g) = 4 g + 32 g 36 g = 36 g Equation is balanced.

11 Balancing A Synthesis Equation Equation: Na + Cl → NaCl A. Diatomic Gas: Cl is a diatomic gas. Na isn ’ t a diatomic gas. Na is a metal. Na + Cl 2 → NaCl Formula of compound balanced? Yes. Na + Cl -

12 Balancing A Synthesis Equation B.Put a “ 2 ” in front of the Na and a “ 2 ” in front of NaCl. Check number of each element again. 2Na + Cl 2 → 2NaCl Na = 2 Na = 2 Cl = 2 Cl = 2 The equation is balanced.

13 Balancing A Synthesis Equation C.Check number of each element on both sides. Na + Cl 2 → NaCl Na = 1 Na = 1 Cl = 2 Cl = 1 Not Balanced.

14 Balancing A Synthesis Equation D. Conservation of Mass 2Na + Cl 2 → 2NaCl (2 x 23)g + 71g = 2( )g 117 g = 117 g

15 Balancing A Single Replacement Equation C.Same elements on both sides NaI + F 2(g) → NaF + I 2 (g) sodium sodium iodine iodine fluorine fluorine

16 Balancing A Single Replacement Equation A.Check for diatomic gases NaI + F → NaF + I F and I are diatomic gases. Add “2” as a subscript on both. NaI + F 2(g) → NaF + I 2 (g)

17 Balancing A Single Replacement Equation B.Balance the formulas of compounds Na I + F 2(g) → Na F + I 2 (g) The compounds, NaI and NaF are balanced.

18 Balancing A Single Replacement Equation D.Same number of atoms or ions on both sides NaI + F 2(g) → NaF + I 2 (g) 1 – Na 1 – Na 1 – I 2 – I 2 – F 1 – F Equation is incorrect.

19 Balancing A Single Replacement Equation “2” is needed in front of NaI and NaF. 2NaI + F 2(g) → 2NaF + I 2 (g) 2 – Na 2 – Na 2 – I 2 – I 2 – F 2 – F Equation is correct.

20 Balancing A Single Replacement Equation E. Same mass on both sides 2NaI + F 2(g) → 2NaF + I 2 (g) 2( )+ 2(19) = 2( ) + 2(127) 338 g = 338 g

21 Balancing A Double Replacement Equation A. Check for diatomic gases. Fe S (s) + H Cl (aq) → H S (g) + Fe Cl (aq) No diatomic gases. Chlorine isn ’ t ALONE.

22 B. Check The Formulas of Compounds All formulas must be balanced. Incorrect: Fe S (s) + H Cl (aq) → H S (g) + Fe Cl (aq) Correct: Fe S (s) + H Cl (aq) → H 2 S (g) + Fe Cl 2(aq)

23 C. Same Elements on Both Sides FeS(s) + HCl (aq) → H 2 S (g) FeCl 2(aq) iron iron sulfur sulfur hydrogen chlorine chlorine

24 D. Conservation of Atoms The number of ions or atoms each element must be the same on both sides Fe S (s) + H Cl (aq) → H 2 S (g) + Fe Cl 2(aq) Reactants Products Fe =1 Fe = 1 S = 1 S = 1 H = 1 H = 2 Cl = 1 Cl = 2 This equation is incorrect.

25 D. What’s Needed? We need 2 hydrogen and 2 chlorine. You can’t write in subscripts. This is incorrect. H 2 Cl 2. This formula isn’t balanced. Hydrogen and chlorine are written with the subscript “2” when they are alone in an equation. You must write the 2 in front of HCl as a coefficient. You have 2-H and 2-Cl.

26 E. Balanced Equation Balanced Formula Fe S (s) + 2HCl (aq) → H 2 S (g) + FeCl 2(aq) Reactants Products Fe =1 Fe = 1 S = 1 S = 1 H = 2 H = 2 Cl = 2 Cl = 2 This equation is correct.

27 F. Law of Conservation of Mass Calculate the total molar mass on each side. They must be equal. Fe S (s) + 2HCl (aq) → H 2 S (g) + FeCl 2(aq) (56+32) + (2 + 71) = (2 +32) + ( ) 88g + 73g = 34g + 127g 161g = 161g


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