r2.1 amount of chemical change

Question 1

what is stoichiometry?

Answer 1

the ratio of the amount of reactants and products in a reaction

Question 2

why do we balance equations?

Answer 2

the law of the conservation of mass states that mass is conserved in a chemical reaction. therefore, there must be the same number of each atom in the reactants and products

Question 3

what are the reacting masses equations?

Answer 3

solid: moles = mass / molar mass
gas: moles = volume / 22.7
aqueous: moles = concentration x volume
liquid: density = mass / volume

Question 4

how do we do reacting masses calculations?

Answer 4

1. balance the equation. identify the known and unknown reactant or product
2. convert the ‘known’ mass, concentration or volume given into moles
3. use the mole ratio of a balanced chemical equation to determine the moles of the unknown value
4. convert the moles into the required quantity

Question 5

what are the limiting and excess reactants?

Answer 5

the limiting reactant is the reactant that limits the amount of products that can be formed.
the excess reactant is the reactant that remains when the limiting reactant is consumed.

Question 6

how do you determine the limiting and excess reactant?

Answer 6

1. determine the amount in moles of each reactant
2. divide the amount of each reactant by its coefficient in the balanced equation
3. the lowest value is the limiting reactant and the highest is the excess reactant

Question 7

what is theoretical yield and actual yield?

Answer 7

the theoretical yield is the maximum amount of product that can be formed in a chemical reaction (based on the stoichiometry of the reaction and amount of the limiting reactant).
the actual yield is the amount of product that is formed in a chemical reaction which may be lower than the theoretical yield.

Question 8

what factors affect percentage yield?

Answer 8

loss of product: some of the product may evaporate or simply be spilled. it may also be lost when isolating or purifying the product.
incomplete reaction: there may be impurities present or the reaction may not go to completion due to insufficient time.
alternative reactions: an unexpected side reaction may occur which results in a different product
one or more of the reactants is impure

Question 9

how do you calculate percentage yield?

Answer 9

percent yield = actual yield / theoretical yield x 100