Topic 3: full set

What is percentage yield?

Percentage yield is the ratio of actual yield to the theoretical yield, expressed as a percentage.

How do you calculate percentage yield?

(Actual yield /. theoretical yield) x100

What is the theoretical yield?

The maximum amount of product that can be obtained from a given amount of reactants, based on stoichiometry.

Why might the percentage yield be less than 100%?

Because of losses during the reaction, side reactions, or incomplete reactions.

How do you determine the actual yield in a reaction?

By measuring the amount of product obtained after the reaction.

Why is it important to calculate percentage yield in industrial processes?

It helps assess the efficiency of reactions and optimize processes.

How do you improve percentage yield in a reaction?

Minimize losses through better reaction conditions, purification, and collection techniques.

How can percentage yield exceed 100%?

If impurities are present in the product, leading to an overestimation of the actual yield.

What is the ideal percentage yield for a reaction?

100%, indicating that all reactants are converted to desired products.

How can excess reactants affect percentage yield?

If excess reactants are present, they may cause incomplete reactions, lowering the yield.

How does the reaction conditions affect the percentage yield?

Optimizing temperature, pressure, and time can increase the likelihood of reaching maximum yield.

How does purity of reactants influence percentage yield?

Impurities can decrease the yield by causing side reactions or reducing the reaction efficiency.

How do you measure the actual yield of a solid product?

Weigh the product after drying to remove any solvent.

How is percentage yield used to assess the success of a chemical process?

It helps evaluate whether a reaction is operating efficiently and economically.

How do you handle discrepancies between actual and theoretical yield?

Identify the causes (e.g., side reactions, incomplete reactions) and optimize the process.

What is atom economy?

Atom economy refers to the percentage of reactants that are converted into useful products.

Why is a high atom economy important?

A high atom economy means less waste and more efficient use of materials.

How do you calculate atom economy?

Atom economy = (M_r of useful products / M_r of all reactants) x100

What does a low atom economy mean?

It means that a lot of the reactants are wasted in the form of by-products.

How can atom economy be improved in a chemical process?

By designing reactions where more of the reactants are turned into useful products.

What is a reaction with a high atom economy?

A reaction with a high percentage of reactants converted to desired products, such as the production of hydrogen from methane.

How can you calculate the atom economy of a reaction with multiple products?

Add the molar masses of useful products, divide by total molar mass of reactants, then multiply by 100.

Why is atom economy important in green chemistry?

It helps minimize waste, reduce environmental impact, and use resources more efficiently.

How does atom economy affect industrial processes?

High atom economy reduces costs, energy use, and waste disposal needs

How does atom economy relate to sustainability?

Higher atom economy supports sustainable chemical processes by reducing waste.

How can you improve atom economy in reactions with multiple by-products?

Use catalysts to maximize the conversion of reactants to desired products.

How do you calculate the molar mass of reactants in atom economy?

Add the molar masses of all reactants involved in the reaction.

How does atom economy affect the cost of producing a product?

Higher atom economy means fewer raw materials are wasted, reducing the cost of production.

Why is atom economy critical in pharmaceutical manufacturing?

It ensures that the maximum amount of active ingredient is obtained with minimal waste.

How do you optimize atom economy in large-scale reactions?

Optimize the reaction conditions to maximize product formation and minimize side reactions.

How do you calculate the molar concentration of a solution?

Molarity = moles of solute / volume of solution in litres

What units are used for concentration?

Concentration is measured in mol/dm³.

How would you calculate the final concentration of a diluted solution?

Use the equation: C1V1=C2V2, where C is concentration and V is volume.

What is the concentration of a solution with 2 moles of NaCl in 4 dm³ of water?

Concentration = 2 mol ÷ 4 dm³ = 0.5 mol/dm³.

How do you convert between molarity and molarity in moles per liter?

1 mol/dm³ is equivalent to 1 mol/L, so they are interchangeable.

How do you calculate the number of moles from concentration and volume?

Use the equation moles=concentration×volume

If you dilute a solution by a factor of 2, how does the concentration change?

The concentration will be halved.

How do you find the volume of a solute in a given concentration and volume?

V₂ = C₁V₁ / C₂

What is the relationship between volume and concentration in a dilution?

Volume and concentration are inversely proportional in a dilution process.

What is the effect of increasing the volume of solvent in a solution?

The concentration of the solution will decrease.

How do you find the concentration of a solution if the moles and volume are known?

Concentration = moles / volume

How would you prepare 1 dm³ of a 1 mol/dm³ NaCl solution from solid NaCl?

Dissolve 58.5 grams of NaCl in water to make 1 dm³ solution.

How can concentration affect reaction rates?

Higher concentrations usually lead to faster reaction rates due to more collisions.

How does the volume of a solution affect its molar concentration?

Decreasing the volume increases the concentration, and increasing the volume decreases it.

How is concentration related to the amount of solute in a solution?

Higher concentration means more solute is dissolved in a given volume of solvent.

What is the relationship between pressure and volume in gases?

They are inversely proportional (Boyle’s Law): as pressure increases, volume decreases.

How does temperature affect the volume of a gas?

As temperature increases, the volume increases (Charles's Law), assuming pressure is constant.

What is the relationship between pressure and temperature in gases?

They are directly proportional (Gay-Lussac’s Law): as temperature increases, pressure increases

How do you calculate the volume of a gas at different temperatures?

Use the equation V1/T1=V2/T2 (Charles’s Law).

What is molar volume?

The volume occupied by 1 mole of a gas at standard temperature and pressure (STP), 24 dm³

How is the ideal gas law expressed?

PV=nRT, where P = pressure, V = volume, n = moles, R = gas constant, T = temperature.

What is the significance of the molar volume at STP?

It allows you to calculate the number of moles from the volume of gas at STP.

How do you calculate the number of moles from the volume of gas?

moles = volume/24

What is the concentration of a solution?

Concentration is the amount of solute in a given volume of solution, usually expressed in mol/dm³.

How do you calculate the concentration of a solution?

Concentration = amount of solute (mol) / volume of solution (dm³)

What is the relationship between moles of solute and concentration?

Moles = concentration × volume.

How do you dilute a solution?

Add solvent to reduce the concentration of solute, while keeping the amount of solute constant.

What is the ideal gas law used for in real-world applications?

It helps calculate gas behavior under various conditions, such as in engines or weather predictions.

What is the unit of concentration in the formula for molarity?

Molarity is measured in mol/dm³ (moles per cubic decimeter).

How do you find the volume of a gas from the ideal gas law?

Rearrange PV=nRT to V= nRT / P to solve for volume

What is a limiting reactant?

A limiting reactant is the reactant that runs out first, stopping the reaction.

How do you identify the limiting reactant in a reaction?

By calculating the amount of product each reactant can produce and identifying which one runs out first.

How can you calculate the limiting reactant from a balanced equation?

Use the mole ratios to determine which reactant will be consumed first based on their amounts.

What happens to the excess reactants after the limiting reactant is used up?

The excess reactants remain unreacted.

How do you determine the amount of product formed using the limiting reactant?

Use the number of moles of the limiting reactant and the mole ratio to find the product.

If 3 moles of hydrogen react with 2 moles of oxygen, what is the limiting reactant?

The limiting reactant is oxygen, as it will be used up first.

What happens to the reaction rate once the limiting reactant is used up?

The reaction stops once the limiting reactant is completely consumed.

How does the amount of limiting reactant affect the yield of a reaction?

The amount of limiting reactant directly determines how much product is formed.

How do you calculate the theoretical yield using the limiting reactant?

Use the mole ratio from the balanced equation to calculate the amount of product formed.

Can the limiting reactant be determined if the quantities of reactants are not given?

No, you need to know the amounts of reactants to determine the limiting reactant.

What is the effect of using excess amounts of one reactant?

Using excess of one reactant does not increase the amount of product formed once the limiting reactant is used up.

How can you improve the yield of a reaction by controlling the limiting reactant?

Ensure the limiting reactant is present in the optimal amount for maximum product formation.

How do you identify the excess reactant in a reaction?

By subtracting the amount of reactant used from the initial amount of excess reactant.

. If 5 moles of A react with 3 moles of B, and the reaction requires a 2:1 ratio of A to B, which is the limiting reactant?

B is the limiting reactant, as the required amount of A (6 moles) is greater than available.

Why is understanding limiting reactants important in industry?

It helps to optimize the use of materials, minimize waste, and improve the efficiency of reactions.

How do you balance chemical equations?

By adjusting the coefficients to ensure the same number of atoms on both sides.

What does the mole in an equation represent?

It represents the ratio of amounts of substances involved in the reaction.

How is the mole related to a balanced equation?

The coefficients in the equation represent the mole ratio of reactants to products.

If 2 moles of hydrogen react with 1 mole of oxygen, what is the mole ratio?

The ratio is 2:1 (H₂ : O₂).

How can you calculate the moles of a product from a chemical equation?

Use the mole ratio from the balanced equation and the number of moles of the reactants.

What is the mole ratio of CO₂ to H₂O in the combustion of methane?

The ratio is 1:2 (CH₄ + 2O₂ → CO₂ + 2H₂O).

How do you use a chemical equation to determine the limiting reactant?

By calculating which reactant runs out first based on the mole ratio and amounts given.

What do you do if the number of moles of a reactant is not given in a reaction?

You can use molar masses to calculate the number of moles from the mass of reactants.

How does the mole ratio help in stoichiometry?

It allows the calculation of the amounts of products formed from given amounts of reactants.

What is the mole of oxygen required to react with 4 moles of hydrogen in the formation of water?

2 moles of oxygen are required for 4 moles of hydrogen (2:1 ratio).

How can you use the mole ratio to determine excess reactants?

By comparing the available amount of reactants with the ratios in the balanced equation.

How do you calculate the moles of carbon dioxide produced in a reaction?

Use the mole ratio from the equation and the amount of reactant involved.

How can you use molar volume to calculate moles of a gas at STP?

Divide the volume of gas by 22.4 dm³ (molar volume) to calculate moles.

How would you use a balanced equation to calculate theoretical yield?

Use the mole ratios to determine how much product should be formed, given the amount of reactants.

What happens when the mole ratio in an equation is not balanced correctly?

The equation no longer represents the correct proportions of reactants and products.

What does the law of conservation of mass state?

Mass cannot be created or destroyed in a chemical reaction.

Why is the mass of reactants equal to the mass of products in a reaction?

Because no atoms are lost or gained during the reaction.

How do you demonstrate conservation of mass in a closed system?

By measuring the mass of the reactants and products in a sealed container.

What happens to the mass in a reaction if there is a gas produced?

The mass of the system remains constant if contained, but may seem to decrease if gas escapes.

How is mass conserved during combustion reactions?

The mass of reactants (fuel + oxygen) is equal to the mass of products (CO₂ + H₂O).

What is a practical example of conservation of mass?

The reaction of magnesium with oxygen forms magnesium oxide, where total mass remains constant.

How can conservation of mass be applied in industrial reactions?

It ensures that materials are used efficiently, and waste is minimized.

Can mass be created or destroyed in nuclear reactions?

No, but nuclear reactions involve a small loss of mass converted to energy.

What happens to the reaction rate if the limiting reactant is increased?

The reaction will continue until the new amount of the limiting reactant is used up.

How can the conservation of mass be used to check the accuracy of reactions?

By comparing the mass of reactants and products and ensuring they are balanced.