Question

A $75\,{\text{g}}$ ice cube is mixed to $450\,{\text{g}}$ of boiling water. Identify the reasons why the water stops boiling immediately:
I. Heat is melting the ice.
II. Condensation is occurring.
III. Phase change occurs.
(A) I only
(B) II only
(C) I and III only
(D) II and III only
(E) I, II, and III

Answer 1

First we will analyse what actually happens when the ice is dropped in a bowl of boiling water. The heat energy is used to melt the ice first until the temperature of mixture becomes equal first.
Complete step by step answer:
In the given question, we are given the following data:
$75\,{\text{g}}$ ice cube is mixed to $450\,{\text{g}}$ of boiling water. In that case we can observe that the water stops boiling immediately. There are many reasons for which this occurs. As soon as you add the ice the heat energy is from the boiling water gets transferred to the ice, which starts changing its phase. As you all know, there are three phases of water namely, ice (which occurs below freezing point) and then comes liquid water (which occurs above the freezing point) and lastly the steam (which occurs as the water begins to boil).
The freezing point of water is $0^\circ {\text{C}}$ and at this temperature liquid water gets converted to ice, i.e. the phase becomes solid and brittle. Just above $0^\circ {\text{C}}$ the ice begins to melt, in the phase changes from solid state to liquid state. Whereas, at $100^\circ {\text{C}}$ , the liquid water begins to boil which produces steam or you can say vapour.
The heat from the boiling water gets transferred to the ice by the phenomenon called conduction. Due to the heat the molecules inside the ice absorb energy from the surrounding medium and start to move faster and are set loose from the strong bonding in the ice.But condensation is the phenomenon in which the gaseous form of water is converted to the liquid form by cooling. This phenomenon has nothing to do with the water to stop boiling immediately.
So, we can conclude that the reasons why the water stops boiling immediately are heat is melting the ice and phase change occurs.
The correct option is C.

Note: The heat which gets transferred from the boiling water to the ice is by conduction. The water present in the bowl will stop boiling until the temperature becomes the same or until the whole ice melts. As soon as the ice melts, the temperature of the resulting solution gets lowered and some more time will be required to elevate its temperature to the boiling point again.