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NSFC Chemistry AQA A level Y13 > Calculation Equations > Flashcards

Calculation Equations Flashcards

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1
Q

Rearrangement of the kinetic energy equation to find the velocity of an atom and units

A

m = mass (Kg); V = velocity (ms-1)

Velocity = √2KE/m

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2
Q

Equation to find the mass of 1 atom

A

mass of 1 atom=Mr/1000/L

Where L is Avogadro’s constant

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3
Q

Relative atomic mass equations

A
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4
Q

Equation that links moles and mass

A

moles = mass(g)/Mr

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5
Q

Equation that links moles and volume in cm3

A

Moles = concentration x (volume[cm3]/ 1000)

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6
Q

Equation that links moles and volume in dm3

A

Moles = concentration x volume[dm3]

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7
Q

Equation that links moles and number of particles

A

Moles = number of particles / Avogadro’s constant

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8
Q

Ideal gas equation and units

A

pV=nRT in the units: P = Pa; V = m3; T = K

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9
Q

How do you convert empirical formula into molecular formula

A

(Mr of molecule/Mr of empirical formula)(empirical formula)

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10
Q

Percentage yield equation

A

%yield = (actual moles of product/theoretical moles of product)(100)

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11
Q

Atom economy equation

A

Atom economy =(Mr of desired product / Mr of all reactants) x 100

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12
Q

Density equation

A

Density = mass / volume

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13
Q

Equation to find the number of outer electrons

A

Group+bonds-charge=number of outer electrons

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14
Q

Equation to find the number of pairs

A

number of outer electrons/2=pairs

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15
Q

Equation to find the number of lone pairs

A

number of Pairs- number of bonding pairs=lone pairs

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16
Q

Mean bond enthalpy equation

A

ΔH = (Σ Bonds broken) – (Σ Bonds formed)

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17
Q

Hess cycle calculation using enthalpy of formation data

A

ΔHr = ΣΔHfθ (products) – ΣΔHfθ (reactants)

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18
Q

Hess cycle calculation using enthalpy of combustion data

A

ΔHr = ΣΔHcθ (reactants) – ΣΔHcθ (products)

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19
Q

Equation to calculate the heat energy of a reaction

A

Q = mCΔT
Where q is the heat energy in Joules,
m is the mass of water heated,
C is the specific heat capacity,
Delta T is the change in temperature in either degrees C or K

20
Q

converting heat energy into enthalpy, units for enthalpy

A

ΔH=Q/1000/n
ΔH is in kJmol-1

21
Q

Generic expression for Kc and units

A

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

You need to derive units for Kc from expression,
[ ] means concentration of

22
Q

Equation for mean bond enthalpy

A

ΔH = Σ(bonds broken) – Σ(bonds formed)

23
Q

What does a negative enthalpy mean? What does a more negative enthalpy show?

A

Enthalpy is exothermic which means heat is released into surroundings, more negative enthalpy means the compound has formed a strong bond/become more stable than what its compared to.

24
Q

What does a positive enthalpy mean? What does a more positive enthalpy show?

A

Enthalpy is endothermic which means heat is taken in from surroundings, more positive enthalpy means the compound has become less stable than what its compared to this means endothermic takes in energy.

25
Q

Equation and units for the calculation of entropy

A

ΔS = Σ(Sproducts) – Σ(Sreactants)

Entropy is in JK-1mol-1

26
Q

What’s the overall Gibb’s Free energy equation? What are the units?

A

ΔG = ΔH – TΔS
Gibbs free energy is usually in kJmol-1,
Enthalpy is in kJmol-1,
T should be in Kelvin (+273 from degrees C)
Entropy is usually in JK-1mol-1 so needs to be divided by 1000

27
Q

How to determine entropy of a reaction from a Graph?

A

use y=mx+c and ΔG = ΔH – TΔS

Plot ΔG on the Y axis
Plot T on the x axis,
ΔH will be the y intercept (C)
– ΔS will be the gradient of the line (m)

28
Q

What assumptions do you make for Gibbs’ free energy if the reaction is feasible or just feasible?
Why is this useful?
What happens to the equations with this assumption?

A

ΔG = 0
It can allow you to find the temperature that reactions will be feasible at,
∆H – T∆S = 0
T = ∆H / ∆S

29
Q

What’s the general equation for the rate of a reaction?

A

Rate = change in concentration / time

30
Q

What’s the general equation for determining a rate constant? What do the symbols mean?

A

For the reaction X + Y –> Z
Rate = k [X]a[Y]b
Where k is the rate constant, [X] is conc. of X, and [Y] is conc. of Y

31
Q

What’s the equation form you need if you want to find out the rate constant or the arrhenius constant?
What do the symbols mean?

A

k = Ae^(-Ea/RT)
Where k is rate constant; A is Arrhenius constant; e is the exponential factor (you’ll find on your calculator), Ea is the activation energy in Jmol-1, R is the ideal gas constant and T is the temperature in K.

32
Q

What’s the equation form you need if you want to find out the activation energy or the temperature constant?
What do the symbols mean?

A

lnk = lnA-Ea/RT
Where k is rate constant; A is Arrhenius constant; ln is the natural log (you’ll find on your calculator with the symbol ln), Ea is the activation energy in Jmol-1, R is the ideal gas constant and T is the temperature in K.

33
Q

How do you calculate a mole fraction?

A

Mole fraction of gas
= gas moles in mixture / total moles of all gases in mixture

34
Q

Equation to find the partial pressure of a gas?

A

Partial pressure of gas = mole fraction of gas x total pressure

35
Q

What’s the equation to calculate the cell emf from a diagram?

A

Emf = E(Rhs) – E(Lhs)
Where ERHS is the right-hand electrode – and ELHS is the left-hand electrode

36
Q

What’s the equation to find the emf of a functioning commercial cell without a diagram?

A

Emf = E(Red) – E(ox)
Where red is the side that’s being reduced and ox is the side being oxidised

37
Q

What’s the equation to calculate pH?

A

pH = –log10[H+]

38
Q

Equation to use for pure water in pH calculations

A

Kw = [H+] [OH–]
Kw = [H+]^2
If not given it/asked to calculate it Kw=10^-14

39
Q

Equation to use for pure strong base in pH calculations

A

Kw = [H+] [OH–]

40
Q

Expression to find the value of Ka,

A

For reaction: HA (aq) ⇋ H+ (aq) + A– (aq)

Ka = [H+ aq] [A– aq]/[HA aq]

Where HA is a weak acid, and Ka is the acid dissociation const

41
Q

Equation to use in buffer calculations/pH of

A

Ka = [H+ aq] [A– aq]/[HA aq]

42
Q

Equation to use in pH calculations to find the pH of a weak acid

A

Ka = [H+ aq] [A– aq]/[HA aq]
Assume [H+]=[A-]
so
Ka=[H+]^2

43
Q

Equation to find pKa from Ka

A

pKa = –log10Ka

44
Q

Equation to find Ka from pKa

A

Ka = 10–pKa

45
Q

Equation to find pH at the half equivalence point with underlying assumption

A

When [HA]=[A-] then… pH = pKa

46
Q

Equation to find the size of the energy gap, with what the symbols mean

A

∆E = hν = hc/λ
∆E = the size of the energy gap (J)
h = planck’s constant
v= frequency (Hz)
c= speed of light in a vacuum (ms-1)
λ= wavelength of light (m)

NSFC Chemistry AQA A level Y13 (41 decks)

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