West Bengal Board Solutions for Chapter: Element, Compound and Chemical Reaction, Exercise 12: Exercise 12

Physical changes can be exothermic or endothermic. Mention three endothermic physical changes from your everyday experience.

When solid ammonium chloride or urea is dissolved in water, drops of water condense on the outer surface of glass test tubes. Can you classify this dissolution process as exothermic or endothermic? What would you see if you dip a thermometer in this solution?

How will you decide whether a change is a chemical reaction or not?

Pouring water on quicklime $\left(\mathrm{CaO}\right)$ generates steam and slaked lime $\left(\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\right)$ is formed. Explain how steam is formed. 

We burn a mixture of oxygen and acetylene gas kept at high pressure for welding metals. Where does the light come from?