1. The Particle Nature of Matter

Avogadro Constant (N_A) 🥑

6.02 × 10²³

Number of particles

N = No. mole x N_A

Relative Atomic Mass (A_r)

The weighted average mass of all isotopes of the element / 1/12 the mass of a ¹²C atom.

Amount of substance

No. mol = Mass (g) / Mr (g/mol)

Molecular formula

Empirical formula multiplied by an integer

Molar Concentration

c = No. mol / Volume (dm³)

cm³ → dm³

Volume (cm³) / 1000

Theoretical yield

Maximum mass of product that could be obtained

Experimental yield

The mass of product obtained

Avogadro’s Law

Equal volumes of gases under the same condition of temperature and pressure contain equal numbers of particles.

No. mol of gas at S.T.P.

No. mol = volume (dm³) / 22.7 (dm³)

Boyle’s Law

Pressure is inversely proportional to volume

Charles’s Law

Temperature is directly proportional to volume

Gay-Lussac’s Law

At constant volume pressure is proportional to temperature

Combined gas law

Ideal gas equation

P(Pa) V(m³) = n(no.mol) R(8.31) T(K)

Why does temperature remain constant at the melting point?

Added energy used to overcome intermolecular forces or the forces of attraction between the particles in the solid lattice. During melting, the average K.E. of the particles does not change.

Melting points of pure substances vs impure substances

Pure substances have sharp melting points.

Impure substances melt over a wider range.

Characteristics of matter

1. Made up of particles, atoms, ions, molecules

2. Occupies a volume in space

3. Has mass

4. Particles are in constant motion

Homogenous mixture

Uniform composition

Heterogenous mixture

Non-uniform distribution of substances.

Calculation empirical formula

1. Ar or Mr

2. % by mass

3. Ratio of atoms (Ar/% by mass)

4. Divide by smallest ratio of atoms

S.T.P.

273K and 1.0 × 10⁵ Pa

Assumptions of the ideal gas model

-Molecules are in constant motion

-Collisions between molecules are perfectly elastic

-Volume occupied by gas is negligible

-No intermolecular forces between molecules

-Kinetic energy of molecules is proportional to temperature