Quantities Used in Chemical Reactions

Quantities in Chemical Reactions

Key Definitions

Mole represents the amount of substance. One mole contains approximately 6.02 x 10^23 particles (Avogadro’s number).
Molecular mass is the mass of one molecule, measured on the scale where the carbon-12 atom has a mass of exactly 12 atomic mass units.
Molar mass (gram formula mass) is the mass of one mole of a substance, expressed in grams per mole (g/mol).
Avogadro’s law states that ‘equal volumes of all gases at the same temperature and pressure contain an equal number of molecules’.

Stoichiometry in Chemical Equations

Stoichiometry is the practice of calculating the relative quantities of reactants and products in chemical reactions.
It’s used to predict how much product can be made from a certain amount of reactant or how much reactant is needed to produce a certain amount of product.
A balanced chemical equation ensures that the law of conservation of mass is observed. The number of each type of atom on both sides of the equation must be equal.
Stoichiometric coefficients in an equation represent the number of moles of each substance.

Calculation of Amounts in Reactions

To calculate the number of moles, the formula moles = mass/molar mass is used.
The theoretical yield is the maximum amount of product that can be formed from a given amount of reactants.
The actual yield is the amount of product actually produced in a chemical reaction.
The percentage yield is a measure of the efficiency of a reaction, calculated using the formula (actual yield/theoretical yield) x 100%.

Limiting and Excess Reactants

The limiting reactant is the reactant that is completely consumed in a chemical reaction and determines the maximum amount of product that can be formed.
The excess reactant is the reactant that is not completely used up in a reaction. It is left over when the limiting reactant is used up.

Concentration in Solution

Concentration is a measure of the amount of solute in a given amount of solution, often expressed in moles per litre (mol/L), or molarity (M).
To calculate concentration, the formula concentration = moles/volume is used.

Establishing a solid understanding of chemical quantities and calculations provides a foundation for comprehending chemical reactions and developing problem-solving skills in chemistry.