Science questions in short. [2 marks ]

Combustion is a chemical process in which a substance reacts with oxygen and gives out energy during the process in the form of either heat or light or both. Rusting of iron is an exothermic process as heat is released during rusting. Hence, it is a kind of slow combustion.

Water extinguishes heat by cooling down the burning substance such as wood and paper. When water is thrown on these substances, it gets cooled below its ignition temperature and also stops burning. The water vapour produced by the action of heat of fire on water surround the burning material and help in cutting off the supply of air.

To put an electrical fire out, we need to unplug or de-energies the equipment on fire. That will eliminate the electricity that is causing the fire. If one cannot unplug what is burning there is a special type of fire extinguisher.

Combustible substance: The substance that undergoes combustion is said to be combustible. Example: Petrol Non-combustible substance: The substance that does not undergo combustion is said to be non-combustible. Example: Iron

The temperature at which a substance catches fire and starts burning is called its ignition temperature.

A small fire like a drum of kerosene on fire can be extinguished by throwing sand or soil over it. When sand is thrown over burning kerosene oil, the sand covers it like blanket. The sand cuts off the air supply to the burning kerosene oil due to which the fire gets extinguished.

The ignition temperature of wood or coal is very high, as it requires too much of time to get heated before burning. We use paper or kerosene to start fire because they have low ignition temperature which helps to catch fire immediately and helps the wood or the coal to reach its required ignition temperature.

When a burning candle is covered with an inverted gas jar, the oxygen supply gets cut-off. Oxygen is necessary for combustion to take place. It is a supporter of combustion. Hence the candle gets extinguished after sometime.

No, it is not correct carbon dioxide does not cause acid rain but it leads to global warming.
Acid rain is caused by oxides of sulphur and nitrogen.

There are three zones in a flame as shown in the following diagram:

The substances which get vapourised during burning gives flames. Charcoal while burning do not vapourise and so does not produce a flame while burning.

A goldsmith blows air into the kerosene lamp flame with a blow pipe so that complete combustion of fuel takes place and the temperature of the flame increases. He blow the outermost zone of a flame with a metallic blow pipe for melting gold and silver because this is the hottest part of the flame.

Food is the fuel for our body because in our body food is broken down by reaction with oxygen and heat is produced.

The reactions which proceed suddenly with the evolution of heat, light and sound along with the formation of a large amount of gas is called explosion.

When magnesium burns with oxygen the products formed are magnesium oxide, heat and light.

One of the necessary condition to continue the process of combustion is the continuous supply of oxygen. When we cover the fire with a blanket or anything we cut-off the supply of air to the fire. Hence, the fire extinguishes.

As water is heavier than petrol therefore slips down permitting the petrol to rise to the surface and continue to burn. Besides, the existing temperature is so high that the water poured on the fire evaporates even before it can extinguisher the fire.

The most common fire extinguisher is water but it could not be used in fire involving electric current and oil.

Supply of oxygen is one of the necessary condition for combustion. Hence, if the supply of oxygen is not sufficient then the fuel will not burn completely.

The above statement is not correct fuels can be in all the three states i.e solid liquid and gas.An example of fuel of each state is:
Solid– Coal. Liquid– Kerosene oil. Gas– Natural gas.

A chemical process in which a substance reacts with the oxygen to give heat and light is called combustion. The light which is given off during combustion can be in the form of flame or as a glow. The substance which undergoes combustion is said to be combustible. It is called fuel.

Due to the burning of coal, the available oxygen gets depleted and it leads to incomplete burning of coal. Incomplete combustion of coal gives carbon monoxide gas. It is a very poisonous gas. It is dangerous to burn coal in a closed room. The carbon monoxide gas produced can kill persons sleeping in that closed room.

Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not because wrapping paper around an aluminium pipe increases its Ignition temperature.

Water is not suitable for fires involving oil and petrol because water is heavier than oil and petrol. Hence, when we spray water on a fire involving oil and petrol the water sinks below the oil and petrol and the oil keeps on burning at the top.

Water extinguishes heat by cooling down the burning substance. When water is thrown on substances, it gets cooled below its ignition temperature and also stops burning. The water vapour produced by the action of heat of fire on water surround the burning material and help in cutting off the supply of air.

If the clothes of a person catch fire, the person should be immediately covered with a blanket. When the burning clothes of a person are covered with a blanket, the supply of air to the burning clothes is cut off and hence the burning stops.

The unburnt wax vapours of a burning candle constitutes the innermost zone of the flame which is least hot.

Combustion is a chemical process in which a substance reacts with oxygen and gives out energy during the process in the form of either heat or light or both. Rusting of iron is an exothermic process as heat is released during rusting. Hence, it is a kind of slow combustion.

A matchstick can light a tiny splinter of wood but not a big log of wood. A splinter of wood has a low ignition temperature. A burning matchstick can produce sufficient heat to reach the ignition temperature of the splinter of wood therefore a matchstick can light a splinter of wood directly.

The type of combustion in which a substance suddenly bursts into flames, without the application of any apparent cause is called spontaneous combustion. Here, phosphorus burns in air at room temperature on its own hence, it is a spontaneous combustion.

A fuel is a very good source of heat. The heat energy produced by burning a fuel can be used directly to cook food, for running motor vehicles and factory machines, can be converted into electrical energy at thermal power stations. Wood and Petrol are examples of two common fuels.