9702 · 15.1
The mole flashcards
Revision flashcards for Cambridge 9702 The mole (syllabus 15.1). Flip, recall, then mark a real past-paper question.
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What is the SI base unit for "amount of substance"?
The mole (mol).
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How is one mole precisely defined?
The quantity of substance containing the same number of elementary entities as there are atoms in exactly 12 grams of Carbon-12.
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What is the value and unit of the Avogadro constant ($N_A$)?
$N_A = 6.02 \times 10^{23} \text{ mol}^{-1}$.
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How do you calculate the total number of particles ($N$) from the number of moles ($n$)?
$N = n N_A$.
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What is molar mass (M)?
The mass of one mole of a substance. Its SI unit is kg/mol, but g/mol is also commonly used.
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How do you calculate the number of moles (n) from mass (m) and molar mass (M)?
$n = m / M$
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What is the molar mass of Carbon-12?
By definition, it is exactly 12 g/mol, or 0.012 kg/mol.
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How many molecules are in 2 moles of water (H₂O)?
Number of molecules = $n \times N_A = 2 \times (6.02 \times 10^{23}) = 1.204 \times 10^{24}$ molecules.
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State the Ideal Gas Equation in terms of the number of moles.
$PV = nRT$.
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What do P, V, n, R, and T represent in $PV = nRT$?
P=pressure, V=volume, n=number of moles, R=molar gas constant, T=absolute temperature.
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What is the value and unit of the molar gas constant ($R$)?
$R = 8.31 \text{ J mol}^{-1} \text{ K}^{-1}$.
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How do you convert Celsius temperature to absolute temperature (Kelvin)?
$T_K = T_C + 273$. (For higher precision, use 273.15)
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State the Ideal Gas Equation in terms of the number of individual molecules.
$PV = NkT$.
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How is the Boltzmann constant ($k$) related to the molar gas constant ($R$) and Avogadro constant ($N_A$)?
$k = R / N_A$.
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What does the Boltzmann constant ($k$) represent?
It relates energy to temperature at the molecular level, or the gas constant per individual particle.