# Gas and Stoichiometry

Please show all work.

1.)(Ideal Gas Law) How many moles of chlorine atoms are there in a container that holds 1.529 kg of XCl5 gas (where X = unknown element) at 600.5°C at a pressure of 1213 torr? The density of the gas is 4.63 g/L.

2.) (Ideal Gas Law) A chemist carries out a reaction and isolates a gaseous product. Analysis shows that each molecule is composed of one phosphorus atom and an undetermined amount of chlorine atoms. Determine the molecular formula of the compound if a 0.515 g sample at a pressure of 923 mm Hg and a temperature of 95.3°C occupies 93.37 mL.

3.) (Gas Stoich.) How many liters of CO2 gas at 45.2°C and 716 torr are formed when 0.485 L of a sample of liquid decane (C10H22) undergoes complete combustion? The density of decane is 0.730 g/mL.

4.) (Dalton's Law Partial P) A sample of solid LiAlH4 reacts with water forming aqueous lithium hydroxide, solid aluminum hydroxide, and hydrogen gas.

a. Write the balanced chemical equation that describes this reaction. Use the correct phase labels for each reactant and product.

b. How many grams of LiAlH4 reacted with an excess of water to produce a sample of hydrogen gas collected over water in a gas collection apparatus at 26.0°C and 0.915 atm in a 1245 mL container?

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#### Solution Preview

1. How many moles of chlorine atoms are there in a container that holds 1.529 kg of XCl5 gas (where X = unknown element) at 600.5°C at a pressure of 1213 torr? The density of the gas is 4.63 g/L.

Response: We need to fill out the PV=nRT equation.

P = (1213 torr)(1 atm/760 torr) = 1.596 atm

V = (1 L/4.63 g)(1.529 Kg)(1000 g/Kg) = 330 L

R = 0.08206 L-atm/mol-K

T = 600.5 C + 273.15 C = 873.65 K

Now, we solve for n (moles).

n = PV/RT

n = (1.596 atm)(330 L)/(0.08206 L-atm/mol-K)(873.65 K) = 7.35 moles XCl5

Since there are 5 atoms of Cl for each molecule of XCl5, there are 7.35 x 5 = 36.8 moles Cl atoms.

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2. A chemist carries out a reaction and isolates a gaseous product. Analysis shows that each molecule is composed of one phosphorus atom and an undetermined amount of chlorine atoms. Determine the molecular formula of the compound if a 0.515 g sample at a pressure of 923 mm Hg and a temperature of 95.3°C occupies 93.37 mL.

Response: We need to fill out the PV=nRT equation.

P = (923 mm Hg)(1 atm/760 mm Hg) = 1.21 atm

V = (93.37 mL)(1 L/1000 mL) = 0.09337 L

R = 0.08206 L-atm/mol-K

T = 95.3 C + 273.15 C = 368.45 K

Now, we solve for n (moles).

n = PV/RT

n = (1.21 atm)(0.09337 L)/(0.08206 L-atm/mol-K)(368.45 K) = 0.00374 moles.

But since we know ...

#### Solution Summary

This solution shows step-by-step calculations to determine the moles of chlorine atoms and molecular formula of the unknown compound using the ideal gas equation. It also determines the liters formed when liquid decane is combusted and reaction of lithium hydroxide with water. All steps are shown with explanations.