Fig. 1 is a heating curve for a pure compound used in reusable hand warmers. A small mass of the solid compound is heated at a constant rate. At the start i...
Question 1 Report
Fig. 1 is a heating curve for a pure compound used in reusable hand warmers. A small mass of the solid compound is heated at a constant rate. At the start it is below its melting temperature. The graph has two flat sections, where the temperature does not increase even though energy is still supplied by the heater.
The manufacturer needs the melting temperature so that the warmer can be stored safely in a car during winter. The compound must not be confused with a mixture, which would usually melt over a range of temperatures.
(a) Use Fig. 1 to state the melting temperature of the compound. [1]
(b) Name the change of state taking place during section B. [1]
(c) Explain why the temperature stays constant during section B. [3]
(d) Describe the differences in particle arrangement and motion between the solid and liquid states. [4]
Answer Details
(a) The melting temperature is 48 0a\(^\circ\mathrm{C}\) [1]. It is read from the first flat section of the heating curve.
(b) Section B shows melting [1].
(c) Energy is still absorbed from the heater [1], but it is used to overcome forces between particles [1]. It is not used to increase the particles' kinetic energy, so the temperature does not rise [1].
(d) In a solid, particles are in a fixed, regular structure [1] and vibrate about fixed positions [1]. In a liquid, particles remain close together but are irregularly arranged [1], and they can move or slide past one another [1].
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