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Topic 5: Chemical formulas and Chemical Equations

20. Balanced equations: Determining which equation demonstrates conservation

1. Which of these equations demonstrates conservation of matter and charge?
1) 2CO + O2 ----- > CO2

3) 2H2 + O2 ------ > H2O

2) 2CO + O2 ----- > 2CO2 4) 2H2 + 2O2 ------ > 2H2O

2. Which of these equations is correctly balanced?
1) Fe (s) + O2 (g) -------- > Fe2O3 (s) 3) 2Fe (s) + 2O2 (g) ----- > Fe2O3 (s)
2) Fe (s) + O2 (g) ----- > 2Fe2O3 (s) 4) 4Fe (s) + 3O2 (g) -------> 2Fe2O3 (s)

3. Which of these equations shows conservation of atoms?
1) KBr ------- > K + Br2 3) CuCO3 --------- > CuO + CO2
2) 2 KClO3 ------ > 2 KCl + 2O2 4) CaCO3 ------- > CO2 + 2CaO

4. Which is a correctly balanced equation for a reaction between hydrogen and oxygen?
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1) H2 (g) + O2(g) ------ > H2O(g) + heat
2) H2 (g) + O2(g) ------- > 2H2O (g) + heat
3) 2H2 (g) + 2 O2(g) ----- > H2Og) + heat
4) 2H2(g) + O2(g) -------- > 2H2O (g) + heat

5. Which equation is correctly balanced?
1) CaO + 2 H2O ---------- > Ca(OH)2

2) NH3 + 2O2 ----------- > HNO3 + H2O
3) Ca(OH)2 + 2H2PO4 --- > Ca3(PO4)2 + 3H2O
4) Cu + H2SO4 --------- > CuSO4 + H2O + SO2

21. Balanced equations: Predicting missing reactant or product

1. Given the incomplete equation:
Which compound is represented by X? 4Fe + 3O2 ---------- > 2X
1) FeO 2) Fe2O3 3) Fe3O2 4) Fe3O4

2. Given the balanced equation: 2Na + 2H2O ----------- > 2X + H2

What is the correct formula for the product represented by the letter X?
1) NaO 2) Na2O 3) NaOH 4) Na2OH

3. Given the incomplete equation:
2N2O5 ----------------- >
Which set of products completes and balances the incomplete equation? 4) 2NO + 2O2
3) 4NO2 + O2

1) 2N2 + 3O2
2) 2N2 + 2O2

4. Given the incomplete reaction:
Ca + _____ -------------- > H2 + CaCl2
Which is the correct formula and coefficient for the substance that completes and balances the
equation? 2) 2HCl 3) HCl2 4) 2HCl2
1) HCl

5. Given the incomplete equation:
4NH3 + 3 O2 --------------- > 2N2 + XH2O

What is the number of moles of water, X, in the equation? 4) 1

2) 4

3) 3
1) 6

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