Gas stoichiometry?

Question

Please help enlighten me on how to solve the following:

1. If 4.000 grams of hydrogen peroxide is placed within a sealed 250 milliliter container at 500 K.

What is the pressure of the oxygen gas produced in atmospheres?

2𝐻2𝑂2 → 2𝐻2𝑂 + 𝑂2

2. Suppose we have the following combustion reaction below. If we are given 2 moles of ethane

at STP, how many liters of CO2 are produced?

2𝐶2𝐻6 + 7𝑂2(𝑔) → 6𝐻2𝑂(𝑙) + 4𝐶𝑂2(𝑔)

Answer 1

(1). Looking at the balanced equation 2H₂O₂ ==> 2H₂O + O₂ we can see that 1 mol of O₂ gas is produced from 2 moles of H₂O₂. So, we will first find out how many moles of H₂O₂ are present, then convert that to moles of O₂ produced. From the moles of O₂ produced, we can then determine the pressure of that O₂ gas.

moles H₂O₂ present: 4.000 g H₂O₂ x 1 mol H₂O₂/34.01 g = 0.12496 moles H₂O₂

moles O₂ produced = 0.12496 mol H₂O₂ x 1 mol O₂/2 mol H₂O₂ = 0.06248 moles O₂ gas produced

To find pressure, we use the ideal gas law PV = nRT and solve for P(pressure)...

P = nRT/V = (0.06248 mol)(0.0821 Latm/Kmol)(500 K)/0.250 L (note the value of R and volume in liters)

P = 10.26 atmospheres

(2). 2C₂H₆ + 7O₂ ==> 6H₂O + 4CO₂ ... balanced equation

From this balanced equation, we see that 2 moles ethane (C₂H₆) produces 4 moles of CO₂.

To convert moles of gas to liters of gas at STP, recall that at STP 1 mol of gas = 22.4 liters.

Thus, we have the following:

4 moles CO₂ x 22.4 liters/mole = 89.6 liters of CO₂ are produced.