Equal masses of P and Cl react according to the following equation:
2P + 3Cl2 --> 2PCl3
Identify which reagent is in excess. Calculate the percent that will remain at the end of the reaction.
How do you identify limiting reagents when there are no quantities listed? You don't.
To determine which reagent is in excess, we need to compare the number of moles of each reagent used in the reaction.
1. Calculate the number of moles for both P and Cl:
- Since the mass of both P and Cl is equal, we can assume they have the same number of moles.
- To calculate the number of moles, divide the mass of P or Cl by their respective molar masses. The molar mass of P (phosphorus) is 30.97 g/mol, and the molar mass of Cl (chlorine) is 35.45 g/mol.
2. Use the balanced equation to determine the stoichiometry between P and Cl:
- For every 2 moles of P, 3 moles of Cl2 are required to react completely and form 2 moles of PCl3.
- This means that the ratio of moles of P to moles of Cl2 is 2:3.
3. Compare the moles of P and Cl2:
- If the ratio of moles of P to moles of Cl2 is less than 2:3, it means that P is the limiting reagent and Cl2 is in excess.
- If the ratio is greater than 2:3, it means that Cl2 is the limiting reagent and P is in excess.
- If the ratio is exactly 2:3, both reagents are present in stoichiometric amounts, and neither is in excess.
4. Calculate the percent that will remain at the end of the reaction:
- If P is the limiting reagent, we need to determine how much Cl2 will be left over.
- Calculate the moles of PCl3 formed based on the balanced equation.
- Subtract the moles of PCl3 formed from the moles of Cl2 initially present to find the leftover moles of Cl2.
- Convert the leftover moles of Cl2 to grams using its molar mass.
- Finally, calculate the percent that remains by dividing the mass of the leftover Cl2 by the initial mass of Cl2, and then multiplying by 100.
Note: The above steps assume that the reaction goes to completion and obey the stoichiometry mentioned in the balanced equation. In reality, reaction conditions and other factors may affect the outcome.
Performing the calculations will provide the necessary information to identify the excess reagent and calculate the percent that will remain at the end of the reaction.