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QLDChemistryQuick questions
Unit 2: Molecular interactions and reactions
Quick questions on Kinetic theory and the gas laws (QCE Chemistry Unit 2)
13short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is kinetic theory of an ideal gas?Show answer
1. Gas particles are in continuous, random, straight-line motion. 2. The particles have negligible volume compared with the volume of the container.
What is pressure from the particle picture?Show answer
Pressure is the total force exerted by particle-wall collisions divided by the wall area. Three things can change pressure:
What is boyle's law?Show answer
At constant temperature, pressure is inversely proportional to volume for a fixed amount of gas.
What is charles's law?Show answer
At constant pressure, volume is directly proportional to absolute temperature.
What is gay-Lussac's law?Show answer
At constant volume, pressure is directly proportional to absolute temperature.
What is combined gas law?Show answer
When more than one variable changes simultaneously (and n is fixed):
What is worked example?Show answer
A 2.50 L sample of air at 20 degrees C and 100 kPa is heated to 80 degrees C and compressed to 1.00 L. Find the new pressure.
What is units and conventions used in QCE?Show answer
QCAA's data sheet lists R = 8.314 J/(mol K) for use with P in kPa and V in L (yielding J units). Get used to the unit set early.
What is using degrees C in a gas law?Show answer
Always convert to Kelvin first. Using degrees C in Charles's law gives nonsense (a sample at 0 degrees C does not have zero volume).
What is confusing direct and inverse proportions?Show answer
Boyle is inverse (P up, V down); Charles and Gay-Lussac are direct (T up, V or P up).
What is forgetting "fixed amount of gas"?Show answer
All four laws assume n is constant. If gas is added or escapes during the change, you cannot use these laws directly.
What is reading P-V or V-T graphs without checking axes?Show answer
A P-V graph is a hyperbola; P-(1/V) is linear. A V-T graph is linear in Kelvin but does not pass through the origin if T is in degrees C.
What is assuming real gases obey the laws exactly?Show answer
They only approximately do, especially at high pressure or low temperature. QCAA usually qualifies questions with "assuming ideal behaviour".