how do you distinquish between a limiting reactant and the excess reactant in a chemical reaction?
b) how do you distinguish between the theoretical yield and actual yield in stoichiometric calculations and how does the value of the theoretical yield generally compare with the value of the actual yield?
c) why are the actual yields usually less than calculated theoretical yields?
a). The limiting reagent is used completely, the other reagent has some remain unreacted in the procedure.
b). Theoretical yield is what you calculate from the balanced equation. It assumes everything goes 100% according to the procedure. The ACTUAL yield is the amount of material you collect when the experiment is performed. How do they compare? USUALLY the actual yield is lower than the theoretical yield.
c). Three reasons (and I'm sure there are others) could be,
1. we haven't invented perpetual motion; i.e., there is ALWAYS some loss; i.e., there is nothing that is 100%.
2. side reactions where another product is produced which reduces the desired product.
3. Losses due to sloppy lab work (spillage, poorly cleaned lab ware such that contaminants are introduced, bumping of solutions, and that kind of thing.
a) To distinguish between a limiting reactant and an excess reactant in a chemical reaction, you need to compare the moles of each reactant present and their stoichiometric ratios. Here's how:
1. Start with a balanced chemical equation for the reaction.
2. Identify the moles of each reactant present in the reaction.
3. Determine the stoichiometric ratio between the reactants by looking at the coefficients in the balanced equation.
4. Compare the actual ratio of the moles of the reactants with the stoichiometric ratio. The reactant that is present in a lower ratio compared to the stoichiometric ratio is the limiting reactant.
5. The reactant that is present in a higher ratio compared to the stoichiometric ratio is the excess reactant.
b) Distinguishing between the theoretical yield and actual yield in stoichiometric calculations involves looking at the calculated and measured quantities in a reaction. Here's how:
1. Theoretical Yield: It is the maximum amount of product that can be obtained based on stoichiometry and assuming complete conversion of the limiting reactant. To calculate the theoretical yield, use the balanced chemical equation and convert the moles of the limiting reactant to moles of the desired product.
2. Actual Yield: It is the amount of product that is obtained experimentally in a reaction. This is determined through laboratory experimentation and measurement.
The value of the theoretical yield tends to be higher than the value of the actual yield. This difference is primarily due to factors such as incomplete reactions, side reactions, impurities, experimental errors, and loss of product during filtration or transfer processes.
c) Actual yields are usually less than calculated theoretical yields due to several reasons:
1. Incomplete reactions: Reactions may not proceed to completion due to factors such as equilibrium limitations or reversible reactions.
2. Side reactions: Unwanted side reactions can occur, consuming some of the reactants and reducing the overall yield of the desired product.
3. Impurities: Contaminants or impurities in the reactants or reaction mixture can interfere with the desired reaction, leading to lower yields.
4. Experimental errors: Errors in measurement, handling, or other experimental procedures can contribute to variations in the actual yield.
5. Losses during separation or purification: During the process of separating or purifying the product, some of it can be lost, resulting in a lower actual yield.
These factors collectively contribute to the difference between the actual and theoretical yields, and are why actual yields are generally lower than the calculated theoretical yields.