MATTER IN OUR SURROUNDINGS

 1. Define the term (a) latent Heat of Fusion (b) latent heat of  vaporization.

(a) Latent heat of fusion, also known as enthalpy of fusion, is the amount of energy that must be supplied to a solid substance (typically in the form of heat) in order to trigger a change in its physical state and convert it into a liquid (when the pressure of the environment is kept constant). For example, the latent heat of fusion of one kilogram of water, which is the amount of heat energy that must be supplied to convert 1 kg of ice without changing the temperature of the environment (which is kept at zero degrees celsius) is 333.55 kilojoules.

(B) Latent heat is defined as the heat or energy that is absorbed or released during a phase change of a substance. It could either be from a gas to a liquid or liquid to solid and vice versa. Latent heat is related to a heat property called enthalpy.

2. State the effect of (I) Surface area (II) nature of the liquid on the rate evaporation

• Surface area : We know that the evaporation of the liquid only happens from the outermost surface of that liquid. And that's why ,the rate of evaporation is directly proportional to the surface area of the liquid. Which means a liquid with greater surface area will have greater evaporation rate and vice versa.

• Nature of liquid : There are two types of liquid according to the nature of evaporation.

1) Volatile

2) Non Volatile

Volatile liquids have much higher evaporation rate than the non volatile liquids. Volatile liquid can evaporate in very short amount of time even in the room temperature and the non volatile liquid needs external heat application for evaporation.

3. Liquids generally have lower density as compared to solids but ice floats on water. Why?

Though ice is a solid it has large amount of space between its molecules. These spaces are larger as compared to spaces in water molecules. Thus the volume of ice is greater than water. Hence the density of ice is less than of water. A substance with low density than water can float on it.