Liquid oxygen at is heated up to at a constant pressure of . The rate of heating is constant. Which one of the following graphs represents the variation of temperature with time?
Graph showing temperature increasing, then remaining constant during phase change, and then increasing again
Graph showing temperature increasing continuously without any constant temperature phase
Graph showing temperature remaining constant initially and then increasing
Graph showing temperature increasing and then remaining constant indefinitely
When liquid oxygen at is heated, its temperature will initially rise until it reaches its boiling point (which is approximately ). During this period, the specific heat of the liquid determines the slope of the temperature-time graph. Once it reaches the boiling point, a phase change from liquid to gas occurs. During this phase transition, the temperature remains constant despite continuous heating, as the heat supplied is used as the latent heat of vaporization. This corresponds to a horizontal line (plateau) on the graph. After all the liquid oxygen has vaporised into gas, the continuous heating will cause the temperature of the gaseous oxygen to rise steadily up to . Therefore, the correct graph must show an initial positive slope, a horizontal plateau at the boiling point, and then another positive slope.
Join thousands of students and practice with AI-generated mock tests.