Tips and Tricks of The Day

Ex: Why a gas has two principal specific heat capacities? Or Gases have two specific heats, but the solids and liquids possess only one specific heat. Why?

 

Solution: When the gases are heated, there occurs an appreciable change in their volume. So energy is required for expansion and we have two specific heats one at constant pressure and the other at constant volume. In case of solids and liquids, expansion is negligible, so they have only one specific heat i.e., at constant volume.

Ex: What is the basic condition for the motion of a particle to be S.H.M.?                     

 

Solution: The motion of a particle will necessarily be simple harmonic if the restoring force acting on it is proportional to its displacement from the mean position i.e., F=−kx.

Ex: What is the ratio of the nuclear densities of two nuclei having mass numbers in the ratio 1:4?

 

Solution: As the nuclear density is independent of mass number, so the ratio of nuclear densities of the two given nuclei is 1:1.

Ex: Water does not come out of a dropper unless its rubber bulb is pressed hard. Why?

 

Solution: Water is held inside the dropper against the atmospheric pressure. When the rubber bulb is pressed, pressure on water becomes greater than the atmospheric pressure and so water comes out.

Ex: Amorphous solids do not melt at a sharp temperature, rather these have softening range. Explain this observation.

 

Solution: All bonds in an amorphous solid are not equally strong. When the solid is heated, weaker bonds get ruptured at lower temperatures and the stronger ones at higher temperatures. So the solid first softens and then finally melts.

Ex: Out of a solid, liquid and gas of the same mass and at the same temperature, which one has the greatest internal energy? Which one least? Justify.

 

Solution: The gas has greatest internal energy because the potential energy (which is negative) of the molecules is very small. On the other hand, the (negative) potential energy of the molecules of a solid is very large; hence the internal energy of solid is least.

Ex: What is the ratio of the nuclear densities of two nuclei having mass numbers in the ratio 1:4?

 

Solution: As the nuclear density is independent of mass number, so the ratio of nuclear densities of the two given nuclei is 1:1.

Ex: When acetylene reacts with HCl in the presence of HgCl₂, the product is:

 

Explanation:

                         HgCl₂

CH ≡ CH + HCl--------> CH₂=CH−Cl

Ex: Is it theoretically possible to device a heat engine which will create no thermal pollution?

 

Solution: No. According to the second law of thermo- dynamics, whole of the heat cannot be converted into work. So a part of the heat that is not converted into work is exhausted by the engine to the atmosphere (sink). Hence thermal pollution will always occur.

Ex: An aqueous solution of iodine becomes colourless on adding excess of sodium hydroxide to it.

 

Solution: An aqueous solution of iodine is violet in colour but it becomes colourless on adding excess of sodium hydroxide because the products formed as a result of chemical reaction are colourless 2NaOH + I₂ -----> NaI + NaIO + H₂O An aqueous solution of iodine becomes colourless on adding excess of sodium hydroxide to it.