The temperature-time graph given below shows the heating curve for pure wax. Study the graph and answer the following questions : (a) What is the physical state of the substance at points A, B, C and D ? (b) What is the melting point of the substance ? (c) What is the boiling point of the substance ? (d) Which portions of the graph indicate that the change of state is taking place ? (e) Name the terms used for heat absorbed during change of states involved in the above process.
CBSE Class IX Science LA (5 Marks)
Answers
(b) 15°C
(c) 110°C
(d) A1B1 and D1D2
(e) Latent heat of fusion and latent heat of vaporization.
Answer:
Explanation:
(a) At point A : The substance is in the solid state. where Solid wax (1/2).
At point B : The substance has started melting. It exists both in the solid and liquid states.
At point C : The substance is in the liquid state.
At point D : The substance has started boiling . It exists both into the liquid and gaseous states.
(b) The melting point of the substance wax is 15°C(1 /2).
(c) The boiling point of the substance wax is = 110°C (1/2).
(d) The A 1 to B 1 and D 1 to D 2 . Or Straight lines in the curve parallel to Time-axis (x-axis) indicate the change of state. These portions are to (Solid to liquid) and to (Liquid to vapor state).
(e) From A 1 to B 1 - latent heat of fusion. D 1 to D 2 - Latent heat of vaporization. During melting, at melting point, the heat absorbed is called latent heat of fusion. During boiling, at boiling point, the heat absorbed is called latent heat of vaporization.