Question

Refer to the plot of temperature versus time showing the changes in the state of ice on heating (not to scale). Which of the following is correct?

(A) AB represents ice and water are not in the thermal equilibrium.
(B) At B water starts boiling.
(C) At C all the water gets converted into steam.
(D) A CD represents water and steam in equilibrium at boiling point.

Answer 1

Hint Temperature is on y axis and time is in X-axis so there will be change in temperature only if there is a slope in the graph and there will be no change in the temperature if there is no slope. If there is no slope which means there will only change in the state of ice.

Step-by-step solution
By considering the graph we have AB, there is no change in temperature which is clear in the graph so there will be the change in the state of ice i.e. ice is melting (from solid state to liquid state).
BC -we can clearly see the change in the temperature which means the temperature of water is now increasing.
CD - we can clearly see that there is no change in the temperature which means there is a change in state of water this time (from liquid state to gaseous state).
Now in DE - we can clearly see that there is change in the temperature. So here we have a change in the temperature of vapour.
Now considering the option (a)->AB represents ice and water are not in thermal equilibrium.
So, by AB we can clearly see that there is equilibrium in the state of ice and water with decrease in the temperature will result in the formation of ice and with increase in the temperature will result in the formation of water. Therefore, option(a) is the wrong option as it is saying that AB is representing that it is not in equilibrium.
Now consider the option(b)-> At B water starts boiling.
So, this option is also incorrect as water starts boiling at 100 degree Celsius which is at point C.
Now consider the option (c)-> At C all the water gets converted into steam.
So, this option is also incorrect as water will get converted to steam at point D.
Now consider the option(d), CD represents water and steam in equilibrium at boiling point.
So, it is true that an increase in temperature will result in formation of vapour and with decrease in the temperature will result in formation of water.

Option (d) is the correct answer.

Note Remember that if there is slope then there will change in temperature of the present state. If there is no slope which means there is no change in the temperature of the state, only state changes and it holds equilibrium. And, try to answer these questions by eliminating options which are easy to work with questions like these.