C1: Formulae and Equations
C1: Formulae and Equations
Empirical and Molecular Formulae
- An empirical formula shows the simplest whole-number ratio of atoms of each element in a compound.
- Molecular formulae indicate the actual numbers of atoms of each type of element present in a molecule.
- To determine the molecular formula from the empirical formula, you'll need to know the relative molecular mass of the substance.
Balancing Chemical Equations
- A balanced chemical equation respects the Law of Conservation of Mass, indicating that matter can neither be created nor destroyed.
- Balancing a chemical equation involves ensuring that the number of each type of atom on the left (reactants) equals the number on the right (products).
- Coefficients (numbers placed before the elements or compounds) are used to balance the equation.
State Symbols in Chemical Equations
- In chemical equations, the state of matter (solid, liquid, gas or aqueous) of reactants and products is often indicated.
- The state symbols are (s) for solids, (l) for liquids, (g) for gases, and (aq) for solutions in water (aqueous).
Using Moles in Calculations
- A mole is the amount of a chemical substance that contains exactly 6.02 x 10^23 particles (Avogadro's number).
- The molar mass (Mr) of a substance is the mass per mole of its entities (atoms, molecules, ions etc.) and it's measured in grams per mole (g/mol).
- The mole concept can be used to calculate amounts of reactants or products in a chemical reaction, or to analyse the composition of a sample.
Stoichiometry
- Stoichiometry involves the calculation of quantities (typically in grams or moles) in chemical reactions.
- It's based on the balanced chemical equation and the concept of molar ratios.
- The limiting reagent is the reactant that is completely consumed in the reaction and determines the maximum amount of product that can be formed.
Percentage Yield and Atom Economy
- Percentage yield compares the actual yield of a reaction to the theoretical yield that could be obtained if all reactants were converted to product.
- Atom economy is a measure of how efficiently the atoms of the reactants are converted into useful product atoms.
- Atom economy is particularly important in green chemistry, where the goal is to minimise waste.