A-Level Chemistry Equations

Ar from isotopes

Ar = Σ(% of isotope X relative mass)

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Mass of an atom

Ar
Mass (g) = ----------
L

L = Avogadro's constant 6.022 X 10²³

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Moles (Solid)

Mass
Mol = -------------
Mr

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Moles (Liquid)

Mol = Volume (dm³) X Conc.

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Moles (Gas ⦵)

Volume (dm³)
Mol = ----------------
24

Any gas under ⦵ has a volume of 24 dm³ mol⁻¹

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Moles (Avagadro)

Particles
Moles = -------------
L

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Ideal Gas Equation

PV = nRT

P = Pressure (kPa)
V = Volume (m³)
n = Moles
R = Ideal Gas constant (8.31 J K⁻¹ Mol⁻¹)
T = Temperature (K (= C + 273)

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% Yield

Actual Yield
% Yield = ------------------ X 100
Theoretical Yield

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Atom Economy

Mr of Desired
Product
Atom Economy = --------------- X 100
Mr of all
Reactants

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Density

Mass
Density = -----------
Volume

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% error

Error
% error = ------------ X 100
Reading

Error =
Theoretical value - Experimental Value

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Rate

Change in conc.
Rate = ---------------------
Time

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Rate (Order)

Rate = k[A]ˣ[B]ʸ

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Arrhenius Equation

(Calculating effect of changing environment on rate)

k = Ae⁽⁻ᴱᵃ/ᴿᵀ⁾
k = rate constant
A = frequency factor (No. and orientation of collisions)
e = on calc.
Ea = activation energy (unit = R*T)
R = universal gas constant
T = Temperature (K)
e⁽⁻ᴱᵃ/ᴿᵀ⁾ = fraction of collisions with Ea (AKA f)

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Arrhenius Equation
(Variable and Units)

k = Rate constant
A = Frequency Factor (Frequency of Collisions)
e = Mathematical Constant (on calc)
Eₐ = Activation energy (J)
R = Gas constant (8.31 J K⁻¹ mol⁻¹)
T = Temperature (K)

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Bond Energy

ΔH = Σ(bonds broken)-Σ(bonds made)

ΔH = Enthalpy change

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Enthalpy of Combustion

ΔH =ΣΔH(reactants)-ΣΔH(products)

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Enthalpy of Formation

ΔH =ΣΔH(products)-ΣΔH(reactants)

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Energy change

q = mcΔT

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

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Kc (eq constant - conc.)

∏[products]ᵐᵒˡᵉˢ
Kc = ------------------
∏[reactants]ᵐᵒˡᵉˢ

∏ means product and is the multiplication equivalent of ∑

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Kp (eq constant - pressure)

∏(p products)ᵐᵒˡᵉˢ
Kp = ------------------
∏(p reactants)ᵐᵒˡᵉˢ

p = partial pressure

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Mole Fraction

Moles of species
Mole fraction = -------------------
Total moles

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Partial Pressure

Partial Pressure =
Mole Fraction X Total Pressure

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Gibbs free energy

(Feasability of reaction)

ΔG=ΔH-TΔS

ΔS = Entropy Change

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Entropy Change (ΔS)

ΔS = Σ(S products)-Σ(S reactants)

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pH (strong acid)

pH = -log₁₀[H⁺]

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[H⁺] (strong acid)

[H⁺] = 10⁻ᵖᴴ

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pH (Strong base)

Kw and [OH⁻] given in the question
Kw = [H⁺][OH⁻]
Kw
[H⁺] = -------
[OH⁻]
pH = -log₁₀[H⁺]

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pH (Weak acid)

Ka = ([H⁺] X A⁻) / HA
In weak acids [H⁺]≈[A⁻]
So
[H⁺]² OR [A⁻]²
Ka = ---------------
[HA](start)
Rearrange to give [H⁺] = √(Ka X [HA(start)])
Then use -log₁₀ [H⁺] to calculate pH

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pH (Weak base)

Kb = ([OH⁻] X [BH⁺]) / B
Assuming [OH⁻] ≈ [BH⁺]
[OH⁻] = √(Kb X [B])
pH = 14 - (-log₁₀ [OH⁻])

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pKa

Pka = -log₁₀(Ka)

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Ka
(From pKa)

Ka = 10⁻ᵖᴷᵃ

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Kw (Ionic product of water)

Kw = [H⁺][OH⁻]

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Ka

[H⁺][A⁻]
Ka = --------------
[HA]

A⁻ = Dissociated acid
HA = Undissociated acid

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New conc. of solution upon addition of solute

moles of solute
New conc. = ------------------- X 1000
new total volume of
solution

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A-Level Chemistry Equations

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