Question

Give reason as to why the density of the substance (except water) decreases with increase in temperature?
A. because the mass of the substance decreases with an increase in temperature.
B. because the mass of the substance increases with an increase in temperature.
C. because the volume of the substance decreases with an increase in temperature.
D. because the volume of the substance increases with an increase in temperature.

Answer 1

Hint: As we go by the definition of the density, it is the mass of a material substance per unit volume. The mass of a body can be calculated from its volume or vice versa using density; the mass is equal to the volume multiplied by the density, while the volume is equal to the mass divided by the density.

Complete answer:
Here, by all kinds of practical examples we have seen that when a substance is heated, it expands and loses density. Between 0°C and 4°C, water compresses rather than expands. At 4°C, water has the highest density. This is referred to as water's anomalous behavior. This kind of exception is only present for water. Other kinds of materials always tend to expand due to separation and more random motion of their molecules.

So, all the substance expands on heating and compresses on cooling but their mass remains unchanged therefore we can see by the relation of mass, volume and density that as mass remains constant and volume increases due to expansion this leads to the decrease in density of the material too.Finally, we can say that as the temperature of the substance increases the density of the substance decreases.

Therefore, the correct option is D.

Note: When we heat any substance except water, their molecular vibration becomes more rapid than before. This leads to the separation of these molecules as the bond between them starts getting weaker. The weaker attraction is only due to separation, there is not any kind of loss in molecules within the material due to which only increase in volume is seen without change in mass.