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chemistry aqa a level > 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

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 released into surroundings, more positive enthalpy means the compound has become less stable than what its compared to.

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)

chemistry aqa a level (12 decks)

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