Solids, Liquids and Gases
5 marks · NormalA glass tube contains a trapped sample of air. The pressure inside is recorded at different temperatures.
Convert the temperature 25°C to Kelvin.
The initial pressure is 100 kPa at 25°C. What is the pressure if the temperature rises to 75°C, assuming the volume and mass of air remain constant? (Give your answer in kPa, to 2 significant figures.)
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) 298 K · must show Celsius to Kelvin
(b) 120 kPa · must show converts both temperatures to Kelvin, uses pressure law formula, correct substitution and calculation
Show mark scheme and worked solution
Marking points
A1 (a) · 1 mark · Correct conversion of 25°C to 298 K.
M1 (b) · 1 mark · Correctly converts 75°C to Kelvin (348 K).
M2 (b) · 1 mark · Writes down or uses the correct formula: P1/T1 = P2/T2.
M3 (b) · 1 mark · Substitutes values and rearranges formula correctly.
A2 (b) · 1 mark · Correct answer to 2 s.f. (accept values 119–122 kPa).
Worked solution
a) Temperature in Kelvin = 25°C + 273 = 298 K.
b) T2 = 75 + 273 = 348 K. Use P1/T1 = P2/T2:
Rounded to 2 significant figures: 120 kPa.