Gas Stoichiometry

Gas Stoichiometry

Moles



Liters of a Gas:

– STP - use 22.4 L/mol – Non-STP - use ideal gas law

Gas Stoichiometry Problem

What volume of CO 2 CaCO 3 forms from 5.25 g of at 103 kPa & 25ºC?

CaCO 3  CaO + CO 2 5.25 g ? L non-STP Looking for liters: Start with stoich and calculate moles of CO 2 .

5.25 g CaCO 3 1 mol CaCO 3 1 mol CO 2

0.052 mols CO 2

100.09g CaCO 3 1 mol CaCO 3 Plug this into the Ideal Gas Law to find liters.

P V = n R T V = n R T P (0.052mol)(8.314kPa L/mol K)(298K) = 103kPa = 1.25 LCO 2

Gas Stoichiometry Problem

How many grams of Al 2 O 3 of O 2 are formed from 15.0 L at 97.3 kPa & 21 °C?

4 Al + 3 O 15.0 L non-STP 2  2 Al 2 O ? g 3 GIVEN: P = 97.3 kPa V = 15.0 L n = ?

T = 21 °C = 294 K R = 8.315

L  kPa/mol  K WORK:

PV = nRT

Given liters: Start with Ideal Gas Law and calculate moles of O 2 .

(97.3 kPa) (15.0 L) = n (8.315

L  kPa/mol  K

) (294K)

NEXT  n = 0.597 mol O 2

Gas Stoichiometry Problem

of O 2 How many grams of Al 2 O 3 from 15.0 L of O 2 are formed at 97.3 kPa & 21 °C?

4 Al + 3 O to grams Al 2 O 3 .

15.0L

Use stoich to convert moles non-STP 2  2 Al 2 O ? g 3 0.597

mol O 2 2 mol Al 2 O 3 3 mol O 2 101.96 g Al 2 O 3 1 mol Al 2 O 3 =

40.6 g Al 2 O 3

Gas Stoichiometry

Find vol. hydrogen gas made when 38.2 g zinc react w /excess hydrochloric acid. @ STP.

Zn (s) + 2 HCl (aq) ZnCl 2 (aq) + H 2 (g) 38.2 g excess X L

What mass solid magnesium is required to react w /250 mL carbon dioxide at 1.5 atm and 77 o C to produce solid magnesium oxide and solid carbon?

2 Mg (s) X g Mg + CO 2 (g) V = 250 mL T = 77 o C oC + 273 = K P = 1.5 atm 2 MgO (s) + C (s) 0.25 L 350 K 151.95 kPa

P V = n R T

n = P V R T n = (0.250 L) 8.314 L .

kPa / mol .

K K (350 K) = 0.013 mol CO 2 CO 2 Mg x g Mg = 0.013 mol CO 2 2 mol Mg 1 mol CO 2 24.3 g Mg 1 mol Mg = 0.63 g Mg

Gas Stoichiometry

How many liters of chlorine gas are needed to react with excess sodium metal to yield 5.0 g of sodium chloride @ STP?

2 Na + Cl

excess X L

2 2 NaCl

5 g

Sample problem 2

Ammonia (NH 3 ) gas can be synthesized from nitrogen gas + hydrogen gas. What volume of ammonia at 450 kPa and 80 °C can be obtained from the complete reaction of 7.5 kg hydrogen?

First we need a balanced equation: N 2 (g) + 3H 2 (g)  2NH 3 (g)

# mol NH 3 =7500 g H 2 x 1 mol H 2 2.02 g H 2 x 2 mol NH 3 3 mol H 2

PV = nRT

= 2475 mol

P = 450 kPa, n = 2475 mol, T = 353 K (2475 mol)(8.31)(353 K) (450 KPa) = V = 16 135 L NH 3

Sample problem 3

Hydrogen gas (and NaOH) is produced when sodium metal is added to water. What mass of Na is needed to produce 20.0 L of H 2 at STP?

First we need a balanced equation: 2Na(s) + 2H 2 O(l)  H 2 (g) + 2NaOH(aq) PV = nRT P= 1atm, V= 20.0 L, T= 273 K (1 atm)(20.0 L) = n = 0.893 mol H (0.0821

atm •L/K•mol )(273 K) or # mol = 20.0 L x 1 mol / 22.4 L = 0.893 mol 2

# g Na= 0.893 mol H 2 x 2 mol Na 1 mol H 2 x 22.99 g Na 1 mol Na = 41.1 g Na