In this combustion reaction of charcoal, you can detect a transfer of thermal energy.
If you walk close to a grill, you will feel the heat given off by the burning charcoal. If you
remove food from the grill with a fork, you will notice that your hand is warmed as you
bring it nearer to the charcoal. The food that is close to the charcoal will be even
warmer. As the food is grilled, its taste and texture change.
Question: Why do you think the food changes as you cook it over the fire?
Question: How do you think a person cooking food on a grill can control the transfer of thermal energy?
Answers
Explanation:
Introduction
People generally use wood, cowdung cakes, crop residues, kerosene oil, coke or LPG gas to cook food. For ruining vehicles, we use petrol or diesel oil. In factories, we use coal or fuel oil or natural gas.
The materials, such as wood, coke, LPG (liquid petroleum gas), petrol, diesel, natural gas have one property [n common, i.e., they produce heat on burning which is then put into different uses. Furthermore, some materials on burning produce flame and some do not. For example, a candle or coal gas on burning produces a flame, but not the coal or charcoal. So, let us study the chemical process of burning and the types of flame produced during this process.
Combustion
Some substances, like magnesium catches fire and burns with a dazzling white flame when heated in air. Similarly, when a piece of per is brought near a candle flame, it burns, producing heat and light. The charcoal and coal bums in air producing carbon dioxide, heat and light.
Air or oxygen which helps in burning is called supporter of combustion and the chemical reaction which takes place with the release of heat and light energy is called combustion.
A chemical process in which a substance reacts with oxygen to give off heat is called combustion.
The substances which undergo combustion are known as combustible substances. It may also be called a fuel.
Sometimes, heat is accompanied by light, either as a flame or as a glow, during combustion.
Fuel may be solid, liquid or gas. A combustion reaction maybe written as-
(a) Charcoal burns in air to give carbon dioxide and heat.
C + O2 → CO2 + Heat
(b) Methane bums in air forming carbon dioxide, water and heat.
CH4 + 2O2 → CO2 + 2H2O + Heat