Acetylene (C2H2) and hydrogen fluoride (HF) react to give difluoroethane:
C2H2+2HF->C2H4F2
When 2.3 mol of C2H2 and 12 mol HF are reacted in a 15.4 L flask, what will be the pressure in the flask at 13°C when the reaction is complete?
I know I'm supposed to find the limiting reagent, and use the formula PV=nRT; but I'm not clear on how to find the limiting reagent yet.
PLEASE HELP!!!
I find the limiting reagent by solving two simple stoichiometry problems. I use one reagent and find the product, then the other reagent and find the product. Convert 2.3 mol C2H4 to moles of the product.
2.3 mols C2H4 x (1 mole C2H4F2/1 mole C2H2) = 2.3 x (1/1) = 2.3 mols C2H4F2.
Then do the same for HF.
12 moles HF x (1 mole C2H4F2/2 moles HF) = 12 x (1/2) = 6 moles C2H4F2
Obviously both answers can't be right; the correct one in limiting reagent problems is ALWAYS the smaller one. In this case, the limiting reagent is C2H2 and there will be 2.3 moles C2H4F2 formed.
To find the limiting reagent, you need to compare the stoichiometric ratio of reactants to determine which one will be completely consumed first. In this case, the stoichiometric ratio between C2H2 and HF is 1:2.
1. Convert the given amounts of C2H2 and HF to moles:
2.3 mol C2H2
12 mol HF
2. Divide the moles of each reactant by their stoichiometric coefficients:
2.3 mol C2H2 / 1 = 2.3 mol C2H2
12 mol HF / 2 = 6 mol HF
Based on the calculations, we can see that C2H2 is the limiting reagent because there are fewer moles of C2H2 compared to the ratio between C2H2 and HF.
Now we can proceed to calculate the pressure in the flask using the ideal gas law equation, PV = nRT:
1. Find the total number of moles of gas present in the flask:
Total moles = 2.3 mol C2H2 + 6 mol HF = 8.3 mol
2. Convert the temperature to Kelvin:
13°C + 273 = 286 K
3. Substitute the values into the ideal gas law equation and solve for pressure (P):
P * 15.4 L = 8.3 mol * 0.0821 atm mol^(-1) K^(-1) * 286 K
P = (8.3 * 0.0821 * 286) / 15.4
P ≈ 12.2 atm
Therefore, the pressure in the flask at 13°C when the reaction is complete is approximately 12.2 atm.
To find the limiting reagent, you need to compare the stoichiometric ratio between the reactants. In this case, the balanced equation tells us that 1 mole of C2H2 reacts with 2 moles of HF.
1. Determine the number of moles available for each reactant:
- Moles of C2H2 = 2.3 mol
- Moles of HF = 12 mol
2. Calculate the number of moles of C2H2 required to react with HF:
- Moles of C2H2 required = 2 * (moles of HF)
- Moles of C2H2 required = 2 * 12 mol = 24 mol
3. Compare the moles available for C2H2 with the moles required:
- Moles of C2H2 available < Moles of C2H2 required
- 2.3 mol < 24 mol
Since the moles of C2H2 available are less than the moles required, C2H2 is the limiting reagent. This means that all 2.3 mol of C2H2 will be completely consumed in the reaction, and the amount of HF is in excess.
To find the pressure in the flask, you can use the ideal gas law equation:
PV = nRT
Where:
P = pressure (in atmospheres)
V = volume (in liters)
n = moles of gas
R = ideal gas constant (0.0821 L.atm/mol.K)
T = temperature (in Kelvin)
1. Convert the temperature to Kelvin:
- Celsius to Kelvin: T(K) = T(°C) + 273.15
- T(K) = 13°C + 273.15 = 286.15 K
2. Determine the moles of the limiting reagent (C2H2), as it will determine the number of moles of the product and hence the pressure:
- Moles of C2H2 = 2.3 mol
3. Plug the values into the ideal gas law equation:
- PV = nRT
- P * 15.4 L = 2.3 mol * 0.0821 L.atm/mol.K * 286.15 K
4. Solve for P (pressure):
- P = (2.3 mol * 0.0821 L.atm/mol.K * 286.15 K) / 15.4 L
Using the correct units and performing the calculation will give you the pressure in the flask at 13°C when the reaction is complete.