Fig. 1 shows a graph from a student’s investigation of a solid wax sample. The student supplied energy at a constant rate and recorded the temperature every...
Question 1 Report
Fig. 1 shows a graph from a student’s investigation of a solid wax sample. The student supplied energy at a constant rate and recorded the temperature every minute. The wax was held in a metal cup. At 4 minutes the temperature stopped rising, although energy was still transferred to the wax. The distance between the heater and the cup was kept constant.
(a) State the state of the wax before point A. [1]
(b) State the melting temperature of this wax. [1]
(c) Explain why the graph is horizontal from 4 minutes to 10 minutes. [3]
(d) Calculate the mean rate of temperature increase during the first 4 minutes. [2]
(e) Describe one difference between the particle arrangement in solid wax and in liquid wax. [1]
Answer Details
(a) Before point A, the wax is a solid. Its temperature is rising until it reaches its melting temperature. [1]
(b) The horizontal section is at 62 °C, so the melting temperature is 62 °C. [1]
(c) Energy continues to be transferred to the wax from 4 minutes to 10 minutes. This energy is used to overcome forces between the particles, allowing the solid to change into a liquid. It is not used to increase particle kinetic energy, so the temperature remains constant and the graph is horizontal. [3]
(d) During the first four minutes, the temperature rises from 20 °C to 62 °C:
\[\text{temperature rise}=62-20=42\text{ °C}\]
\[\text{mean rate of increase}=\frac{42\text{ °C}}{4\text{ min}}=10.5\text{ °C/min}\]
The mean rate is 10.5 °C per min. [2]
(e) In solid wax, particles are in fixed regular positions. In liquid wax, particles remain close together but can move past one another. [1]
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