4.3 Theoretical Yield, Actual Yield and Percent Yield

This topic explains the concepts of theoretical yield, actual yield, and percent yield in chemical reactions. It shows how to calculate the efficiency of a chemical reaction.

Definition

Theoretical Yield: The amount of product calculated from a balanced chemical equation, assuming 100% conversion of the limiting reactant.

Actual Yield: The amount of product actually obtained from a chemical reaction in the laboratory.

Percent Yield: The ratio of actual yield to theoretical yield, expressed as a percentage.

Main Idea

In chemical reactions, the amount of product actually obtained (actual yield) is often less than the amount calculated from the balanced equation (theoretical yield). This is because some reactant may not react, some product may be lost during handling, or side reactions may occur. The efficiency of a reaction is measured by the percent yield.

Core Concept

Percent Yield = Actual YieldTheoretical Yield × 100

• Theoretical yield is the maximum possible product.
• Actual yield is the experimentally obtained product.
• Percent yield tells us how efficient the reaction is.

Detailed Explanation

Theoretical Yield

• We adopted an optimistic approach to the amount of product resulting from the chemical reaction.
• We assume that 100% of the limiting reactant becomes product.
• The amount of product as calculated from the balanced chemical equation is called the theoretical yield.

Actual Yield

• In reality, the amount of products during chemical reactions does not match what the chemical equation shows.
• This is because:
• Some side reactions produce alternative products.
• Some of the product may remain in solution.
• The reaction may be stopped before completion.
• Some product may be lost during handling.
• The amount of product actually obtained is called the actual yield.

Percent Yield

• Percent yield = Actual yieldTheoretical yield × 100
• It measures the efficiency of a chemical reaction.
• A higher percent yield means a more efficient reaction.

Example Calculation

Problem: A reaction has a theoretical yield of 50 g. The actual yield obtained is 40 g. Calculate the percent yield.

Solution:

Percent Yield = Actual YieldTheoretical Yield × 100

Percent Yield = 4050 × 100 = 80\%

Final Answer: Percent yield = 80%

Intermediate Level

Definitions

Why Actual Yield < Theoretical Yield

• Side reactions: Produce alternative products.
• Incomplete reaction: Reaction may not go to completion.
• Loss during handling: Product may be lost during filtration, transfer, etc.
• Impure reactants: Reactants may not be 100% pure.

Formula

Percent Yield = Actual YieldTheoretical Yield × 100

Example

• Theoretical yield = 50 g
• Actual yield = 40 g

Required: - Percent yield

Solution: Percent Yield = 4050 × 100 = 80\%

Final Answer: 80%

Important Points

• 1. Theoretical yield = calculated from balanced equation.
• 2. Actual yield = obtained experimentally.
• 3. Percent yield = ActualTheoretical × 100.
• 4. Actual yield < theoretical yield due to side reactions, incomplete reactions, and loss during handling.
• 5. Example: Theoretical = 50 g, Actual = 40 g → Percent yield = 80%.

Remember

• - Theoretical yield: Maximum possible product
• - Actual yield: Experimentally obtained product
• - Percent yield: ActualTheoretical × 100
• - Actual < Theoretical due to side reactions, incomplete reactions, loss during handling

Common Mistakes

• 1. Confusing theoretical and actual yield: Theoretical = calculated; Actual = experimental.
• 2. Forgetting to multiply by 100: Percent yield is a percentage.
• 3. Thinking actual yield can be greater than theoretical yield: It cannot (in most cases).
• 4. Ignoring the reasons for lower actual yield: Side reactions, incomplete reactions, loss during handling.

Quick Revision

• Theoretical yield = calculated from balanced equation.
• Actual yield = obtained experimentally.
• Percent yield = ActualTheoretical × 100.
• Actual yield < theoretical yield due to side reactions, incomplete reactions, and loss during handling.
• Example: Theoretical = 50 g, Actual = 40 g → Percent yield = 80%.

60-Second Revision

• Theoretical yield: Maximum possible product
• Actual yield: Experimentally obtained product
• Percent yield: ActualTheoretical × 100
• Actual < Theoretical due to side reactions, incomplete reactions, loss during handling

QUALITY VALIDATION

• Topic: 4.3 Theoretical Yield, Actual Yield and Percent Yield
• Chapter: 4 (Stoichiometry)

• Source re-read: PASS
• Source scope followed: PASS
• Knowledge level matched: PASS
• Important concepts covered: PASS
• Definitions checked: PASS
• Equations checked: PASS
• Derivations checked: N/A
• Examples checked: PASS
• Unsupported knowledge added: NO
• Unnecessary repetition: NO
• Notes format maintained: PASS
• Important source content omitted: NO

• Source limitations:
• NONE

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Key Points from the Textbook

• The amount of product as calculated from the balanced chemical equation is called the theoretical yield.
• In reality, the amount of products during chemical reactions does not match what the chemical equation shows because:
• Some side reactions produce alternative products.
• Some of the product may remain in solution.
• The reaction may be stopped before completion.
• Percent yield = Actual yieldTheoretical yield × 100