# 4.7: Unit 4 Practice Problems


### Problem 1.

Balance the following equations:

1. PCl5(s)+H2O(l)→POCl3(l)+HCl(aq)
2. Cu(s)+HNO3(aq)→Cu(NO3)2(aq)+H2O(l)+NO(g)
3. H2(g)+I2(s)→HI(s)
4. Fe(s)+O2(g)→Fe2O3(s)
5. Na(s)+H2O(l)→NaOH(aq)+H2(g)
6. (NH4)2Cr2O7(s)→Cr2O3(s)+N2(g)+H2O(g)

PCl5(s)+H2O(l)→POCl3(l)+2HCl

3Cu(s)+8HNO3(aq)→3Cu(NO3)2(aq)+4H2O(l)+2NO(g)

H2(g)+I2(s)→2HI(s)

4Fe(s)+3O2(g)→2Fe2O3(s)

2Na(s)+2H2O(l)→2NaOH(aq)+H2(g)

(NH4)2Cr2O7(s)→Cr2O3(s)+N2(g)+4H2O(g)

### Question 2.

Write the balanced chemical equation for the combustion of gaseous butane, C4H10.

2C4H10(g)+13O2(g)→8CO2(g)+10H2O(g)

### Question 3.

What is the mass of 0.54mole of CO2?

$\mathrm{0.54\: \cancel{mole} \times \dfrac{44\: g}{1\:\cancel{mole}}=24\: g}$

### Question 4.

230 grams of O is how many moles of O?

$\mathrm{230\: \cancel{g} \times \dfrac{1\: mole}{16\:\cancel{g}}=14\: mole O}$

### Question 5.

What is the mass of 1.00 mole of magnesium nitrate?

The formula for magnesium nitrate is Mg(NO3)2     mass = (1 x 24.31) + (2 x 14.01) + (6 x 16.00) = 148 g Mg(NO3)2

### Question 6.

How many atoms are on 1.76 moles of phosphorus?

$\mathrm{1.76\: \cancel{mole} \times \dfrac{6.02e23\: atoms}{1\:\cancel{mole}}=1.06e24\: atoms}$              1.06x1024atoms

### Question 7.

What is the mass of 3.57x1024molecules of CaS?

### Question 8.

Automotive air bags inflate when a sample of sodium azide, NaN3, is very rapidly decomposed.

2NaN3(s)→2Na(s)+3N2(g)

If this reaction begins with only 1.46 moles of NaN3, how many moles of nitrogen gas, N2, will be produced?

### Question 9.

What mass of silver oxide, Ag2O, is required to produce 25.0 g of silver sulfadiazine, AgC10H9N4SO2, from the reaction of silver oxide and sulfadiazine?

2C10H10N4SO2+Ag2O→2AgC10H9N4SO2+H2O

= 8.11 g Ag2O

### Question 10.

Identify the energy graphs A and B as being for an endothermic or exothermic reaction.

A.

B.