Equations

Question 1

Moles from mass

Answer 1

n = m / Mᵣ

Moles = Mass ÷ Molar Mass

Question 2

Ideal Gas Equation

Answer 2

pV = nRT

P in Pa, V in m³, T in K, R = 8.314 J mol⁻¹ K⁻¹

Question 3

Concentration (mol dm⁻³)

Answer 3

c = n / V

Volume in dm³

Question 4

Dilution calculations

Answer 4

c₁V₁ = c₂V₂

Use when diluting solutions

Question 5

Energy transfer

Answer 5

q = mcΔT

q = heat energy (J), m = mass (g), c = specific heat capacity (J g⁻¹ K⁻¹), ΔT in K

Question 6

Enthalpy change per mole

Answer 6

ΔH = q / n

Enthalpy change in kJ mol⁻¹

Question 7

Bond enthalpy calculation

Answer 7

ΔH = ∑(Bond breaking) - ∑(Bond making)

Bond breaking = endothermic (+), Bond making = exothermic (-)

Question 8

Rate equation

Answer 8

Rate = k[A]ᵐ[B]ⁿ

m & n = orders of reaction

Question 9

Equilibrium constant (Kc)

Answer 9

Kc = [C]ᶜ[D]ᵈ / [A]ᵃ[B]ᵇ

Use equilibrium concentrations

Question 10

pH of strong acids

Answer 10

pH = -log[H⁺]

[H⁺] in mol dm⁻³

Question 11

[H⁺] from pH

Answer 11

[H⁺] = 10^(-pH)

Rearranged pH equation

Question 12

pH of weak acids (Ka expression)

Answer 12

Kₐ = [H⁺]² / [HA]

Approximation for weak acids

Question 13

H+ of buffers

Answer 13

[H+] = Ka x [HA] / [A-]

Question 14

Kw (ionic product of water)

Answer 14

Kw = [H⁺][OH⁻]

Kw = 1.00 × 10⁻¹⁴ mol² dm⁻⁶ at 25°C

Question 15

pH of strong bases

Answer 15

[H⁺] = Kₕ / [OH⁻]

Find H⁺, then use pH equation

Question 16

Electrode potential (E° cell)

Answer 16

E° cell = E° cathode - E° anode

E cell = reduced - oxidised

More positive E° is the reduction reaction

Question 17

Entropy change (ΔS)

Answer 17

ΔS = ∑S products - ∑S reactants

Units = J K⁻¹ mol⁻¹

Question 18

Gibbs Free Energy (Thermodynamics)

Answer 18

ΔG = ΔH - TΔS

If ΔG < 0, reaction is feasible

Question 19

Rate constant (k) from 1/2 life

Answer 19

k = ln2 / t1/2

Question 20

pKa

Answer 20

Question 21

Ka

Answer 21