Question

A mixture of two gases, 0.01mol of C4H10(g) and 0.065mol of O2(g), is pumped into a cylinder with a movable piston, as shown above. The mixture, originally at 200°C and 1.0atm, is sparked and the reaction represented below occurs. 2C4H10(g)+13O2(g)→8CO2(g)+10H2O(g) Which of the following is true after the product gases return to the original temperature and pressure, and why will the change occur? (Assume all gases behave ideally.) answer choices The piston will be higher than its original position, because the cylinder will contain a greater number of gas molecules. The position of the piston will be unchanged, because the total mass of the gases in the cylinder does not change. The position of the piston will be unchanged, because the temperature and pressure of the contents of the cylinder remain the same. The piston will be lower than its original position, because the product molecules are smaller than the reactant molecules.

Answer 1

After the combustion reaction of C4H10 and O2, the number of gas molecules increases from 0.075 mol to 0.09 mol. Under constant temperature and pressure, this means that the volume occupied by the gases increases. Therefore, the piston will be higher than its original position.

Step-by-step explanation:

The student's question pertains to the behavior of gases within a piston after a chemical reaction takes place. Given the chemical reaction 2C4H10(g) + 13O2(g) → 8CO2(g) + 10H2O(g), we can calculate the number of moles of each reactant and product.

Starting with 0.01 mol of C4H10 and 0.065 mol of O2, only 0.005 mol of C4H10 will react because there is not enough O2 to react with all the C4H10 (we would need 0.065 mol of O2 for every 0.01 mol of C4H10 according to the stoichiometry of the balanced equation). This reaction produces 0.04 mol of CO2 and 0.05 mol of H2O.

We originally had 0.01 + 0.065 = 0.075 mol of gases, and after the reaction, we have 0.04 + 0.05 = 0.09 mol of gases. Since the number of moles determines the volume a gas occupies at a given temperature and pressure (according to the ideal gas law), the piston will be higher than its original position after the reaction because the cylinder will contain a greater number of gas molecules.

Answer 2

The position of the piston will be unchanged, because the total mass of the gases in the cylinder does not change.

Step-by-step explanation:

The position of the piston will be unchanged, because the total mass of the gases in the cylinder does not change.

According to the ideal gas law, PV=nRT, where P is the pressure, V is the volume, n is the number of moles of gas, R is the ideal gas constant, and T is the temperature. Since the temperature and pressure of the contents of the cylinder remain the same, and the moles of gas on both sides of the reaction are equal, the volume will remain unchanged.