Topic 3 | Quantitative Chemistry Flashcards
What is the law of conservation of mass?
The law of conservation of mass states that no atoms are lost or made during a chemical reaction, so the mass of the products equals the mass of the reactants.
Why must chemical equations be balanced?
Chemical equations must be balanced to ensure that the number of atoms of each element is the same on both sides of the equation, in accordance with the law of conservation of mass.
How is the relative formula mass (Mr) of a compound calculated?
The relative formula mass (Mr) of a compound is the sum of the relative atomic masses of the atoms in the numbers shown in the formula.
For example, for HCl, Mr = 1 + 35.5 = 36.5.
Why might a reaction appear to involve a change in mass?
A reaction might appear to involve a change in mass if a reactant or product is a gas and its mass has not been accounted for, such as when a gas is released into the atmosphere.
What is a mole in chemistry?
A mole is a unit used to measure the amount of a substance. One mole of a substance contains the same number of particles (atoms, molecules, or ions) as one mole of any other substance, which is 6.02 × 10^23 particles (Avogadro’s constant).
How is the molar mass of a substance related to its relative formula mass (Mr)?
The molar mass of a substance in grams is numerically equal to its relative formula mass (Mr).
For example, the Mr of iron is 56, so one mole of iron weighs 56 grams.
How do you convert grams to moles?
To convert grams to moles, use the formula: moles = mass / molar mass.
For example, to find the number of moles in 42g of carbon, moles = 42 / 12 = 3.5 moles.
How can you use moles to balance a chemical equation?
To balance a chemical equation, convert the masses of reactants and products to moles, then use the mole ratios to determine the simplest whole number ratios for the balanced equation.
What is a limiting reactant?
A limiting reactant is the reactant that is completely used up in a chemical reaction, limiting the amount of product that can be formed.
How is the concentration of a solution measured?
The concentration of a solution can be measured in mass per unit volume, such as grams per cubic decimeter (g/dm³).
What is percentage yield?
Percentage yield is the amount of product obtained from a reaction expressed as a percentage of the maximum possible amount. It is calculated as: (actual yield / theoretical yield) x 100.
What is atom economy?
Atom economy is a measure of the proportion of reactants that end up as useful products. It is calculated as: (Mr of desired product / sum of Mr of all reactants) x 100.
How is concentration measured in mol/dm³?
Concentration in mol/dm³ is calculated using the formula: concentration = moles / volume (in dm³).
What is the volume of one mole of gas at room temperature and pressure (RTP)?
At RTP (20°C and 1 atmosphere pressure), one mole of any gas occupies 24 dm³.
How do you calculate the volume of gas produced in a reaction at RTP?
To calculate the volume of gas produced at RTP, use the formula: volume (dm³) = moles of gas x 24.
For example, if 5 moles of hydrogen gas are produced, the volume is 5 x 24 = 120 dm³.
How do you calculate the theoretical mass of a product?
To calculate the theoretical mass of a product, first calculate the moles of the reactant using moles = mass / molar mass, then use the balanced equation to find the moles of the product, and finally calculate the mass of the product using mass = moles x molar mass.
Why might a reaction not go to completion?
A reaction might not go to completion if it is reversible, meaning some of the reactants are converted back into products, reducing the overall yield.
How do mole ratios help in balancing equations?
Mole ratios from a balanced chemical equation help determine the proportions of reactants and products, allowing you to calculate the amounts of substances involved in the reaction.
What is Avogadro’s constant?
Avogadro’s constant is the number of particles (atoms, molecules, or ions) in one mole of a substance, which is 6.02 × 10^23 particles per mole.
How do you calculate the concentration of a solution if you know the moles and volume?
To calculate the concentration of a solution, use the formula: concentration = moles / volume (in dm³).
