# IB Chemistry Calculations Setting out Templates IB Chemistry Calculations setting out templates

Topic 1 Stoichiometric relationships

SL & HL

Percent composition

M(AB) = ___g/mol

M(A) = ___g/mol

Percentage mass = ___/___ x 100% = ___%

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Empirical and molecular formulae

n(A) = ___g/___gmol-1 = ___mol

n(B) = ___g/___gmol-1 = ___ mol

A___B___

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Ideal gas law

PV = nRT

___ Pa x ___ m3 = ___ mol x 8.314 JK-1 mol-1 x ___ K

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Stoichiometry

aA + bB  cC + dD

or / or
n(A)
= m/M
= ___g / ___ g/mol
= ___mol A / 1 mol gas : 22.7dm3
X : ___dm3
∴X = ____ mol A / n(A)
= CV
= ___mol/dm3 x ___ dm3
= ___ mol A

a mol A : c mol C

___ mol A : X

∴X = ____ mol C

or / or
m(C)
= nM
= ___ mol x ___ g/mol
= ___ g C / 1 mol gas : 22.7dm3
___ mol C : X
∴X = ____ dm3 C / C(C)
= n/V
= ___mol / ___ dm3
= ___ mol/ dm3 C

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Topic 4 Chemical bonding and structure

HL only

Formal charge

First draw Lewis dot structure

FC (___) = valence e- – ½ bonding e- – non-bonding e-

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Bond order

First draw Lewis dot structure

Bond order = total number of bonding pairs/total number of positions

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Bond calculations

Ephoton = hf

v = fλ

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Topic 5 Energetics and thermochemistry

SL & HL

Heat of reaction and enthalpy

aA + bB  cC + dD

Q = mcT

= ___ g x 4.18Jg-1ᵒC-1 x ___ᵒC

= ___ kJ

H = Q/n

= ___kJ/___moles = ___ kJ/mol

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Hess’ Law

aA + bB  cC + dDH = ___ kJ (reverse etc…)

aA + bB  cC + dDH = ___ kJ (X2 etc…)

______

aA + bB  cC + dDH = ___ kJ

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Enthalpy of formation

aA + bB  cC + dD

ΣΔHoproducts = (c x ____) + (d x ___) = ___ kJ

ΣΔHoreactants = (a x ___) + (b x ___) = ___ kJ

ΔHoformation = ΣΔHoproducts – ΣΔHoreactants = ______- ______= ______kJ

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Enthalpy of combustion

aA + bB  cC + dD

ΣΔHoproducts = (c x ____) + (d x ___) = ___ kJ

ΣΔHoreactants = (a x ___) + (b x ___) = ___ kJ

ΔHocombustion = ΣΔHoreactants – ΣΔHoproducts = ______- ______= ______kJ

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Bond enthalpies

EQUATION DRAWN IN STRUCTURAL FORMULA FORM:

aA + bB  cC + dD

Bonds broken = (a x ___) + (b x ___) = ___ kJ

Bonds formed = (c x ____) + (d x ___) = ___ kJ

ΔHo = ΣΔHoreactants – ΣΔHoproducts = ______- ______= ______kJ

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HL only

Born Haber cycles

M+(g) + X(g)

↑HIE HEA

M(g) + X(g)

↑HatmXM+(g) + X-(g)

M(g) + 1/2 X2(g)

↑HatmM

M(s) + 1/2 X2(g) Hlat

Hf

MX(s)

Hf = HatmM + HatmX + HIE + HEA - Hlat

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Enthalpy of solution and hydration

M+(g) + X-(g)

Hhyd

Hlat M+(aq) + X-(aq)

Hsol

MX(s)

Hlat = Hsol - HhydX- - HhydM+

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Entropy

aA + bB  cC + dD

ΣΔSoproducts = (c x ____) + (d x ___) = ___ J/Kmol

ΣΔSoreactants = (a x ___) + (b x ___) = ___ J/Kmol

ΔS⁰ = ∑ ΔS⁰ (products) - ∑ ΔS⁰ (reactants) = ______- ______= ______J/Kmol

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Gibbs free energy from individual values

aA + bB  cC + dD

ΣΔGoproducts = (c x ____) + (d x ___) = ___ kJ/mol

ΣΔGoreactants = (a x ___) + (b x ___) = ___ kJ/mol

ΔG⁰ = ∑ ΔG⁰ (products) - ∑ ΔG⁰ (reactants) = ______- ______= ______kJ/mol

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Gibbs free energy from entropy and enthalpy

aA + bB  cC + dD

ΔG⁰ = ΔH⁰ - TΔS⁰ = _____ - ______= ______kJ

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Topic 6 Chemical kinetics

SL & HL

Reaction rate

aA + bB  cC + dD

Rate = Δ[P]/t or Δ[R]/t = _____ mol dm-3 s-1

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HL only

Rate equation

aA + bB  cC + dD

When [B] is kept constant [A] is _____.Therefore the order of reaction with respect to A is ____.

When [A] is kept constant [B] is _____. Therefore the order of reaction with respect to B is ____.

rate = k[A]?[B]?

Units of k = (mol.dm-3s-1) / order of reaction value x (mol.dm-3)

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Activation energy

ln(k) = Ea/RT + lnA

(Graph ln(k) by 1/T in Kelvin by first making a table if not already done)

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Topic 7 Equilibrium

SL & HL

Only writing the equilibrium constant

aA + bB ⇌ cC + dD

Kc = [C]c[D]d / [A]a[B]b (at equilibrium)

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HL only

Reaction quotient

aA + bB ⇌ cC + dD

Q = [C]c[D]d / [A]a[B]b (NOT at equilibrium)

Q is >/< K therefore reaction moves to the left/right.

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The equilibrium constant

aA + bB ⇌ cC + dD

[A] / [B] / [C] / [D]
R / a / b / c / d
I
C
E

Kc = [C]c[D]d / [A]a[B]b

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Gibbs free energy and equilibrium

∆G° = -RTlnK

K is >1 therefore favourable etc….

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Topic 8 Acids and bases

HL only

Calculating pH for weak acids and bases

HA(aq) ⇌ H+(aq) + A-(aq)

[H+]2 = [HA]Ka

pH = - log [H+(aq)] = ____

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Topic 9 Redox processes

SL & HL

Balancing redox half equations

Step 1MO  M (balance atoms besides H and O)

Step 2 2+ 0(oxidation states)

Step 3 MO + 2e-  M (balance electrons)

Step 4 MO + 2e- + 2H+  M (balance charges with H+)

Step 5 MO + 2e- + 2H+  M + H2O (H2O for final balancing)

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Combining redox half equations

Step 1M  MO + e- Oxidation

NO + e-  NReduction

Step 2 M  MO + e- Oxidation multiplied by ____

NO + e-  NReduction multiplied by ____

Step 3 NO + M + e-  MO + N + e- Add

Step 4 NO + M  MO + N Simplify

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HL only

Determining cell potentials with E⁰ values

A+ + e- ⇌ A E⁰=____

B+ + e- ⇌ B E⁰=____

Write and reverse the least positive value

A+ + e-  A E⁰=____

B  B+ + e- E⁰= (-)____

A+ + B  A + B+ E⁰= ____

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Products of electrolysis

Ions present:

A+, B+, H2O

A+ + e- ⇌ A E⁰=____

B+ + e- ⇌ B E⁰=____

½O2(g) + 2H2(aq) + 2e- ⇌ H2O(l) E⁰= + 1.23

H2O(l) + e- ⇌ ½H2(g) + (aq) + OH-(aq)E⁰= - 0.83

Cathode: (take most positive)

A+ + e-  A E⁰=____

H2O(l) + e- ⇌ ½H2(g) + (aq) + OH-(aq)E⁰= - 0.83

Anode: (take most positive)

B  B+ + e- E⁰= (-)____

H2O(l) ⇌ ½O2(g) + 2H2(aq) + 2e-E⁰= - 1.23

E⁰=____

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Determining cell potentials with Gibbs

If necessary, setting out as above to work out E⁰, then

ΔG⁰ = -nFE⁰

or

E = E⁰ – (RT/nF)lnQ

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Quantitative electrolysis

Q = It

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Topic 11 Measurement and data processing

SL & HL

Percent error

Percent error = ((Theoretical result - experimental result)/Theoretical result) x 100%

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Propagation of uncertainty

Add uncertainties for + and - . Add percent uncertainties for x and divide. Don’t forget significant figures. Final absolute uncertainty has only 1 sig fig.

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Index of Hydrogen Deficiency

For CcHhNnOoXx

IHD = (0.5)(2c+2-h-x+n)

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