Introduction to the particulate nature of matter and chemical change
Nature of Matter
- Everything that has mass and occupies space is known as matter.
- Atoms are the smallest indivisible particles of matter that take part in chemical reactions.
- Atoms combine in different ways to form molecules which are the smallest particles of a substance that retains its identity and properties.
- Atoms and molecules compose matter existing in three states: solids, liquids, and gases.
- The state of matter can change due to the change in temperature and pressure, however, the chemical composition remains the same.
Molecular and Empirical Formulas
- A molecular formula shows the actual number of atoms of each element in a molecule of a compound.
- Empirical formula shows the simplest ratio of atoms of each element in a compound.
- For instance, glucose has a molecular formula of C6H12O6 and an empirical formula of CH2O.
Balanced Equations and Stoichiometry
- A chemical equation represents a chemical reaction where the reactants are written on the left-hand side, the products on the right, and an arrow pointing from reactants to products.
- Balancing an equation involves ensuring that the law of conservation of mass is satisfied, i.e., the number of atoms of each element is the same on both sides of the equation.
- Stoichiometry deals with the calculation of quantities (in moles, mass, or volume) of reactants and products in a balanced chemical equation.
Mole Concept and Avogadro's Number
- The mole is a unit of amount of substance in chemistry, which contains as many entities as there are in 12 grams of carbon-12, equal to Avogadro’s number.
- Avogadro's number is 6.022 x 10^23 and is the number of atoms in one mole of any substance.
- The mole concept allows for the calculation of amounts of substance involved in chemical change, given the molar mass and quantity in moles, mass, or volume.
Limiting Reactants
- In a chemical reaction, the limiting reactant is the substance that is totally consumed when the reaction is 100% complete.
- It determines the maximum amount of product that can be formed and the amount of reactant left over.
- To identify the limiting reactant, compare the mole ratio of the amount of reactants used with the mole ratio of the balanced chemical equation.