Chemical Yield and Stoichiometry

A set of flashcards covering definitions, calculations, and practical considerations related to chemical yield, theoretical yield, actual yield, percentage yield, limiting reagents, and industrial efficiency factors.

What is chemical yield?

The amount of product actually obtained from a chemical reaction.

What is theoretical yield?

The maximum amount of product that can be formed from given amounts of reactants, calculated from the balanced equation assuming complete conversion and no losses.

What is actual yield?

The quantity of product that is actually collected after the reaction and any purification steps.

How do you calculate percentage yield?

Percentage yield = (actual yield ÷ theoretical yield) × 100%.

Why is the percentage yield often less than 100%?

• Reaction may not go to completion.
• Side reactions may form unwanted products.
• Product can be lost during purification, transfer, or handling.
• Measurement or weighing errors can occur.

Can percentage yield ever be more than 100%, and why?

Yes. Impurities, residual solvents, or measurement errors can make the measured (apparent) mass of product larger than the theoretical value, giving a yield over 100%.

How do you calculate the theoretical yield from given reactant amounts?

1. Write and balance the chemical equation.
2. Calculate moles of each reactant.
3. Determine the limiting reactant using stoichiometric ratios.
4. Use the limiting-reactant moles and stoichiometry to find moles of desired product.
5. Convert product moles to mass with its molar mass.

What is the limiting reagent in a reaction?

The reactant that is completely consumed first, thereby limiting the amount of product that can form.

How do you identify the limiting reagent?

• Calculate moles of each reactant.
• Use stoichiometry to find how many moles (or mass) of product each reactant could produce.
• The reactant that would produce the least amount of product is the limiting reagent.

How can chemical yield affect industrial processes?

• Low yields waste raw materials and raise production costs.
• Higher yields improve efficiency and profitability.
• Maximizing yield also reduces environmental impact by minimizing waste generation.

Besides yield, what other factors are important for assessing reaction efficiency?

• Atom economy (proportion of reactant atoms incorporated into the desired product).
• Reaction rate.
• Cost, availability, and safety of reactants and products.