Question

501
use for melting gold and silver
and why?
In an experiment 4.5 kg of a fuel was completely burnt. The heat produced
was measured to be 180,000 kJ. Calculate the calorific value of the fuel
Can the process of rusting be called combustion? Discuss
Abida and Ramesh were doing an experiment in which water was to be
heated in a beaker. Abida kept the beaker near the wick in the yellow part
of the candle flame. Ramesh kept the beaker in the outermost part of the
flame. Whose water will get heated in a shorter time?​

Answer 1

Answer:Q.1.  List conditions under which combustion can take place. Ans. Conditions necessary for combustion are:           (i) Presence of a combustible substance.           (ii) Attainment of ignition temperature.           (iii) Proper supply of air to provide oxygen.

Q.2.  Fill in the blanks.           (a) Burning of wood and coal causes _________ of air.           (b) A liquid fuel used in homes is _________.           (c) Fuel must be heated to its_________before it starts burning.           (d) Fire produced by oil cannot be controlled by_________.Ans. (a) pollution                                    (b) kerosene.           (c) ignition temperature           (d) water.

Q.3.  Explain how the use of CNG in automobiles has reduced pollution in our cities. The use of CNG in place of petrol and diesel reduce pollutions in following ways:           (i) It produces less carbon monoxide gas.           (ii) It produces less carbon dioxide gas.           (iii) It produces less amount of sulphur dioxide and nitrogen dioxide which cause acid rain.           (iv) No residue remains after combustion.

Explanation: