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Yield & Atom Economy (AQA GCSE Chemistry)

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  • What does percentage yield compare?

    Percentage yield compares the actual yield to the theoretical yield.

  • Define actual yield.

    Actual yield is the recorded amount of product obtained from a chemical reaction.

  • How is the actual yield determined?

    The actual yield can be determined by experiment only.

  • What is theoretical yield?

    Theoretical yield is the amount of product that would be obtained under perfect practical and chemical conditions.

  • What type of calculation lets you determine the theoretical yield?

    The type of calculation lets you determine theoretical yield is a reacting mass calculation.

  • State the equation for percentage yield.

    The equation for percentage yield is:

    (actual yield divided by theoretical yield) x 100

  • True or False?

    A high percentage yield is desirable for economic reasons.

    True.

    For economic reasons, the objective is to have as high a percentage yield as possible to increase profits and reduce costs and waste.

  • If the actual yield is 1.50 g and theoretical yield is 2.00g, what is the percentage yield?

    If the actual yield is 1.50 g and theoretical yield is 2.00g, the percentage yield is:

    (1.50 divided by 2.0) x 100 = 75%

  • What factors can reduce the percentage yield of a reaction?

    Factors that can reduce percentage yield include:

    • Incomplete reactions

    • Side reactions

    • Loss during processing

    • Reversible reactions.

  • What are the steps to calculate theoretical mass of products?

    (Higher tier only)

    The steps to calculate theoretical mass of products are:

    1. Write balanced equation.

    2. Convert given mass to moles.

    3. Use coefficients to find moles of product.

    4. Convert moles of product to mass.

  • What is the formula to calculate moles from mass?

    The formula to calculate moles from mass is:

    Moles = mass / molar mass

  • True or False?

    Coefficients in a balanced equation are used to calculate molar masses.

    False.

    Coefficients in a balanced equation are not used to calculate molar masses. Molar masses are calculated from chemical formulae.

  • What is the formula to calculate mass from moles?

    The formula to calculate mass from moles is:

    Mass = moles × molar mass

  • True or False?

    The theoretical yield can only be determined by experiment.

    (Higher tier only)

    False.

    The theoretical yield can be calculated assuming 100% conversion of reactants to products.

  • How do you determine the molar ratio between reactants and products?

    The molar ratio is determined by the coefficients in the balanced chemical equation.

  • What is the purpose of calculating theoretical masses of products?

    (Higher tier only)

    Calculating theoretical masses of products allows for comparison with actual yields and determination of percentage yield.

  • What is atom economy?

    Atom economy is a measure of the efficiency of a chemical reaction in terms of how well reactants are utilised to produce useful products.

  • What information does atom economy give about a reaction?

    Atom economy tells us what percentage of the mass of reactants become useful products.

  • What is the equation that is used to calculate atom economy?

    To calculate atom economy:

    Atom economy = fraction numerator T o t a l space M subscript r space o f space d e s i r e d space p r o d u c t over denominator T o t a l space M subscript r space o f space a l l space p r o d u c t s end fraction cross times 100

  • What is the atom economy of the following reaction?

    N2 (g) + 3H2 (g) ⇌ 2NH3 (g)

    The atom economy for N2 (g) + 3H2 (g) ⇌ 2NH3 (g) is 100% as there is only one product.

  • True or False?

    The higher the atom economy of a process then the more sustainable that process is.

    True.

    The higher the atom economy of a process then the more sustainable that process is

  • What is the atom economy for the production of CaO in the following reaction?

    CaCO3 → CaO + CO2

    Mr CaCO3 = 100, Mr CaO = 56, Mr CO2 = 44

    The atom economy for the production of CaO in the reaction is 56%.

  • How can the atom economy of a reaction be increased?

    The atom economy of a reaction can be increased by selling the by-products of the reaction.

  • What is the atom economy for the production of ethene?

    C2​H2​ + H2 ​→ C2​H4​

    The atom economy for the production of ethene is 100%.

  • True or False?

    Higher atom economy indicates more waste generation.

    False.

    Higher atom economy means less waste production.

  • Why is waste reduction in chemical processes important?

    Waste reduction in chemical processes is important because it minimises environmental impact and is more sustainable.

  • How does atom economy relate to waste production?

    A lower atom economy indicates more waste production in a reaction.

  • How can atom economy be improved?

    Atom economy can be improved by finding uses for by-products or choosing reaction pathways with fewer unwanted products.

  • What does an atom economy of 100% indicate?

    An atom economy of 100% indicates that all atoms from the reactants end up in the desired product.

  • List four factors considered when choosing a reaction pathway.

    Four factors considered when choosing a reaction pathway are:

    • Atom economy

    • Percentage yield

    • Rates of reaction

    • Equilibrium position

  • Why are reactions with low atom economies unsustainable?

    Reactions with low atom economies are unsustainable because they use up too much raw material to manufacture only a small amount of product.

  • True or False?

    Fast reaction rates are desirable in industrial chemical processes.

    True.

    Fast reaction rates are desirable in industrial chemical processes.

  • How can the position of equilibrium be changed in reversible reactions?

    The position of equilibrium can be changed by altering reaction conditions.

  • True or False?

    High percentage yields are undesirable in industrial processes.

    False.

    High percentage yields are desirable in industrial chemical processes.

  • What is the benefit of selling or reusing waste products?

    Selling or reusing waste products can improve the atom economy of a reaction.

  • Why do companies continually analyse reactions and processes?

    Companies continually analyse reactions and processes to improve efficiency and reduce costs.

  • What is the relationship between atom economy and raw material usage?

    Higher atom economy means more efficient use of raw materials and less waste production.

  • How can alternative methods of production improve atom economy?

    Alternative methods of production can improve atom economy by producing more useful by-products.

Previous:Calculating Mass of SubstancesNext:Concentration of Solutions

    1. Topic 1

      Simple Model of the Atom

    2. Topic 2

      The Periodic Table

    3. Topic 3

      Properties of Transition Metals

    1. Topic 1

      Ionic, Covalent & Metallic Bond

    2. Topic 2

      Bonding & Substance Properties

    3. Topic 3

      Structure & Bonding of Carbon

    4. Topic 4

      Bulk & Surface Properties

    1. Topic 1

      Measurement, Mass & Equations

    2. Topic 2

      Calculating Mass of Substances

    3. Topic 3

      Yield & Atom Economy

    4. Topic 4

      Concentration of Solutions

    5. Topic 5

      Amount of Substance & Gas Volume

    1. Topic 1

      Reactivity of Metals

    2. Topic 2

      Reactions of Acids

    3. Topic 3

      Electrolysis

    1. Topic 1

      Exothermic & Endothermic Reactions

    2. Topic 2

      Chemical Cells & Fuel Cells

    1. Topic 1

      Rate of Reaction

    2. Topic 2

      Reversibility & Equilibrium

    1. Topic 1

      Hydrocarbons: Fuel & Feedstock

    2. Topic 2

      Reactions of Alkenes & Alcohols

    3. Topic 3

      Synthetic & Natural Polymers

    1. Topic 1

      Purity, Formulations & Chromatography

    2. Topic 2

      Identification of Common Gases

    3. Topic 3

      Methods of Identifying Ions

    1. Topic 1

      Formation of Earth's Atmosphere

    2. Topic 2

      CO2 & CH4 as Greenhouse Gases

    3. Topic 3

      Causes of Atmospheric Pollution

    1. Topic 1

      Global Reserves & Potable Water

    2. Topic 2

      Life Cycle Analysis & Recycling

    3. Topic 3

      Using Materials

    4. Topic 4

      Haber Process & NPK Fertilisers