1. Explain how and when a pure substance can absorb heat energy and not change i

Question

1. Explain how and when a pure substance can absorb heat energy and not change in temperature? What is really happening?

2. Draw a Lewis structure for CH3OH and formaldehyde (H2CO). Use your knowledge of phases and intermolecular forces to predict which liquid would have a higher vapor pressure , boiling point, surface tension, viscosity, and solubility in water.

3. Why does it take longer to cook an egg in boiling water in Mexico City than in NYC?

4. How does surfactant reduce the surface tension of water and how is it effective in removing stains in clothing?

5. Branched hydrocarbons have lower melting points than straight chain hydrocarbons and tend to be more volatile. Branched carbons also help fuel, burn hotter. Explain the chemistry behind this.

Explanation / Answer

Ans 1 :

Adding heat usually increases the temperature of the substance , so heat and temperature are usually used interchangeably.

But manier times adding heat does not change the temperature of the substance. This happens at the boiling point of the substance.

For example , when the water is heated at its boiling point , the temperature of the water does not increase more tha 100oC , but it changes its physical form from the liquid to the gaseous state.

This heat energy is utilised by the water not to raise the temperature but to break the bonds between the liquid molecules so that the particles can escape from the surface and get converted into steam.

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