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.