Lakhmir Singh and Manjit Kaur Solutions for Chapter: Sources of Energy, Exercise 5: Questions Based on High Order Thinking Skills (HOTS)

The calorific values of three fuels A, B and C are $33 \mathrm{k}\mathrm{J} {\mathrm{g}}^{-1},48 \mathrm{k}\mathrm{J} {\mathrm{g}}^{-1}$ and $150 \mathrm{k}\mathrm{J} {\mathrm{g}}^{-1}$, respectively. A is solid, B is liquid and C is a gas at room temperature. On combustion, both A and B produce carbon dioxide while C explodes forming steam. B and C leave no residue after combustion while A leaves behind some solid residue. Which one of the three fuels is the most ideal? Give two reasons to support your answer.

Calorific value and ignition temperature of fuel X are $75 \mathrm{k}\mathrm{J} {\mathrm{g}}^{-1}$ and $20 \mathrm{℃}$ respectively. These values for fuel Y are $50 \mathrm{k}\mathrm{J} {\mathrm{g}}^{-1}$ and $75 \mathrm{℃}$ respectively. On burning, the fuel Y produces only $\mathrm{C}{\mathrm{O}}_2$ while fuel X produces ${\mathrm{C}\mathrm{O}}_2$ and $\mathrm{C}\mathrm{O}$. Which of the two is a better fuel? Give two reasons to support your answer.

The calorific values of five fuels A, B, C, D and E are given below:
Which of the fuels could be: (i) cooking gas (ii) alcohol (iii) wood (iv) hydrogen (v) kerosene?
A         $48 \mathrm{k}\mathrm{J} {\mathrm{g}}^{-1}$
B        $17 \mathrm{k}\mathrm{J} {\mathrm{g}}^{-1}$
C        $150 \mathrm{k}\mathrm{J} {\mathrm{g}}^{-1}$
D         $50 \mathrm{k}\mathrm{J} {\mathrm{g}}^{-1}$
E         $30 \mathrm{k}\mathrm{J} {\mathrm{g}}^{-1}$

Arrange the following fuels in the order of decreasing calorific values (keeping the fuel with highest calorific value first).
Biogas, Kerosene, Wood, Petrol, Hydrogen gas, Methane

Arrange the following fuels in the order of increasing calorific values (keeping the fuel with lowest calorific value first):
LPG, Coal, Alcohol, Dung cakes, Diesel

Most of the fuels contain carbon as one of the constituents. Name a fuel which has very high calorific value but does not contain carbon.

(Choose from Hydrogen, Nitrogen, Helium)