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Yield and atom economy of chemical reactions (chemistry only)
This chemistry-only topic connects conservation of atoms to practical reaction efficiency, sustainability, economics and data-based choice of reaction pathway.
19
Objectives
95
Flashcards
95
Questions
90 min
Study time
AQAGCSEChemistryQuantitative chemistry
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Syllabus checklist
What you need to know
19 objective pages available
Percentage yield10 objectives
- (chemistry only) Define yield as the amount of product obtained from a reaction.
- (chemistry only) Define percentage yield as the actual amount of product obtained compared with the maximum theoretical amount as a percentage.
- (chemistry only) Calculate percentage yield from actual yield and theoretical yield.
- (chemistry only) Explain why a reaction may not go to completion because it is reversible.
- (chemistry only) Explain why some product may be lost when separated from a reaction mixture.
- (chemistry only) Explain why yield may be reduced if reactants take part in unexpected reactions.
- (chemistry only) Use ratios, fractions and percentages in yield calculations. (MS 1c)
- (chemistry only) Use an appropriate number of significant figures in percentage-yield answers. (MS 2a)
- (chemistry only) Rearrange percentage-yield formulae where required. (MS 3b)
- (chemistry only) (HT only) Calculate theoretical mass of product from a given mass of reactant and a balanced equation.
Atom economy9 objectives
- (chemistry only) Define atom economy as a measure of the amount of starting materials that end up as useful products.
- (chemistry only) Explain why reactions with high atom economy are important for sustainable development.
- (chemistry only) Explain why reactions with high atom economy can be economically important.
- (chemistry only) Calculate atom economy for a reaction to form a desired product from a balanced equation.
- (chemistry only) Identify the desired product when calculating atom economy.
- (chemistry only) Use ratios, fractions and percentages in atom-economy calculations. (MS 1c)
- (chemistry only) Rearrange atom-economy relationships where required. (MS 3b)
- (chemistry only) (HT only) Explain why a reaction pathway is chosen using data such as atom economy, yield, rate, equilibrium position and usefulness of by-products.
- (chemistry only) Distinguish atom economy from percentage yield when evaluating a reaction.
Key terms
YieldPercentage YieldPercentage yieldTheoretical yieldActual yieldReversible reactionCompletion of reactionProduct lossyieldunexpected reactionsSignificant figuresatom economy
Exam tips
- Understand Yield Definition: Calculate carefully by clearly define yield as the amount of product obtained from a reaction in your answers. Link your answer to Percentage yield in Yield and atom economy of chemical reactions (chemistry only), and show formula, substitution, calculation, final answer, and unit where relevant.
- Understand Percentage Yield: Calculate carefully by clearly define percentage yield as the actual yield divided by the theoretical yield, multiplied by 100. Link your answer to Percentage yield in Yield and atom economy of chemical reactions (chemistry only), and show formula, substitution, calculation, final answer, and unit where relevant.
Common mistakes
- Confusing Yield Definition: Clarify that yield specifically refers to the actual amount of product obtained from a reaction, not the theoretical maximum.
- Confusing Percentage Yield with Actual Yield: Remember that percentage yield is a comparison of the actual yield to the theoretical yield expressed as a percentage, not just the actual yield itself.
Practice preview
- For Percentage yield, which option best supports this Unit 4.3 objective: (chemistry only) Define yield as the amount of product obtained from a reaction?
- For Percentage yield, which answer check answer best supports this Unit 4.3 objective: (chemistry only) Define yield as the amount of product obtained from a reaction?
- For Percentage yield, which option best supports this Unit 4.3 objective: (chemistry only) Define percentage yield as the actual amount of product obtained compared with the maximum theoretical amount as a percentage?
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