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OCR A A-Level Inorganic Chemistry > Equations > Flashcards

Equations Flashcards

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1
Q

How do you calculate the relative atomic mass of an element?

A
  • (mass number of isotope 1 × abundance) + (mass number of isotope 2 × abundance), etc./ 100
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2
Q

What is the ideal gas equation?

A
  • pV= nRT
  • p= pressure (Pascals, Pa)
  • V= volume (m^3)
  • n= amount of substance (moles, mol)
  • R= ideal gas constant: 8.314 (J mol^-1 K^-1)
  • T= temperature (Kelvin, K)
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3
Q

What is the equation for percentage yield?

A
  • (Actual yield/ theoretical yield) x100
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4
Q

How is atom economy calculated?

A
  • (sum of molar masses of desired products/ sum of molar masses of all products) x100
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5
Q

How do you calculate percentage uncertainty?

A
  • [(Uncertainty × multiplied by how many readings you take) ÷ (amount recorded)] × 100
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6
Q

How is enthalpy change calculated?

A
  • Bond enthalpies of reactants - bond enthalpies of products
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7
Q

What is the formula to calculate heat energy, and what do each of the symbols stand for? Include units.

A
  • q = mcΔT
  • q: heat energy (J)
  • m: the mass that changes temperature (g)
  • c: the specific heat capacity of the substance that changes temperature
  • ΔT: change in temperature measured
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8
Q

How is rate of reaction calculated? What is its units?

A
  • Change in concentration/ change in time
  • Its units are therefore mol dm^-3 s^-1
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9
Q

What is the rate equation?

A
  • rate = k [A]^m [B]^n
  • k= rate constant
  • A and B: reactants
  • m: order of reaction with respect to A
  • n: order of reaction with respect to B
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10
Q

How can the rate constant for a first order reaction be calculated from a concentration-time graph?

A
  • ln(2) / t1/2
  • Use a concentration-time graph to find the rate of reaction
  • Divide the rate by the concentration at that time
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11
Q

What is the Arrenhius equation? Include units.

A
  • k= A e^ (-Ea / RT)
  • k: rate constant
  • A: pre-exponential/ frequency factor
  • Ea: activation energy (J mol^-1)
  • R: gas constant
  • T: temperature in Kelvin
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12
Q

How can A and Ea be calculated if you have a table of k and T values?

A
  • ln(k) = -Ea / R x 1/T + ln(A)
  • y = mx +c
  • Plot a graph of ln(k) against the reciprocal of time
  • The gradient is -Ea/ R (remember to divide by 1000 at the end)
  • The y-intercept is ln(A)
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13
Q

How is the partial pressure of a gas calculated?

A
  • You multiply the mole fraction of the gas by the total pressure
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14
Q

What are the 2 ways of finding the mole fraction of a gas? Explain.

A
  • The number of moles of the gas can be divided by the total number of moles in the gas mixture
  • Similarly, since under the same conditions the same number of moles of gases take up the same volume, the mole fraction can also be calculated by dividing the volume of the gas by the total volume of the gas mixture
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15
Q

How do you calculate the concentration of hydrogen ions from pH values? How is this rearranged to calculate pH from the concentration of hydrogen ions?

A
  • [H+] = 10^-pH
  • pH = - log [H+]
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16
Q

How can you calculate the pH of a strong, monobasic acid if given its concentration?

A
  • Since the ratio of the acid and the hydrogen ions is 1:1 in the equation of their dissociation, they have the same concentration
  • You can put this value into the equation to find the pH of a solution
17
Q

How do you convert between Ka and pKa?

A
  • pKa= -logKa
  • Ka= 10^-pKa
18
Q

How can Ka be rewritten when considering weak acids?

A
  • Ka= [H+]^2/ [HA] (start)
19
Q

What is the formula for Kw, and therefore its units?

A
  • Kw = [H+][OH-]
  • mol^2 dm^-6
20
Q

How is the pH of strong bases calculated?

A
  • In monoacidic bases like NaOH, their concentration is equal to the concentration of hydroxide ions (in the equation of their dissociation, they’re in a 1:1 ratio)
  • You then use the equation for Kw to calculate [H+], and therefore the pH
21
Q

How do you calculate the pH of a buffer solution? What shortcut is there to this method?

A
  • [H+]= Ka × [HA] / [A-]
  • You can use the moles of HA and A- if it’s faster, since they would have the same volume
22
Q

How is the entropy change of a reaction calculated?

A
  • ΔS⦵ = ΣS⦵(products) - ΣS⦵(reactants)
23
Q

What equation can be used to calculate whether a reaction is feasible? Include units.

A
  • The Gibbs’ equation
  • ΔG = ΔH - TΔS
  • ΔG in kJ mol^-1
  • ΔH in kJ mol^-1
  • T in K
  • S in kJ K^-1 mol^-1

OCR A A-Level Inorganic Chemistry (16 decks)

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