CHEMISTRY [2 Mark Question Answer]

Necessary Conditions for Combustion

• Presence of a combustible substance.
• Presence of a supporter of combustion.
• Heating the combustible substance to its ignition temperature.
• The presence of fuel plays an important role.
• The presence of air or oxygen

a chemical reaction initiated by the absorption of energy in the form of light. The consequence of molecules’ absorbing light is the creation of transient excited states whose chemical and physical properties differ greatly from the original molecules.

• change in color- eg- when lead nitrate is added to potassium sulphate , the precipitate so formed is in yellow in color.
•change in state. …
• change in temperature. …
• evolution of gases. …
• formation of precipitate.

Thermal dissociation is conventionally understood to be a breakdown of chemical bonds in molecules resulting in production of smaller molecules or atoms under the influence of temperature.
Thermal decomposition is breaking a compound into two or more elements, or into two new compounds with the help of heat. These reactions are irreversible. Thermal dissociation is breaking a substance into two or simpler substances with the help of heating.

A reversible reaction is a reaction in which the conversion of reactants to products and the conversion of products to reactants occur simultaneously
The conditions that a reversible process becomes irreversible are: (i) When there is an escape of the gas products through an open system. (ii) If we continuously remove the products formed in the reaction.

A reaction between an acid and base which results in the formation of salt and water is a neutralization reaction. A reaction where a semi-solid insoluble product is formed, which is called precipitate is a precipitation reaction.

Decomposition reactions are also known as analysis reactions or chemical breakdowns. The opposite of this type of reaction is a synthesis in which simpler reactants combine to form a more complex product

A synthesis reaction is a type of reaction in which multiple reactants combine to form a single product. Synthesis reactions release energy in the form of heat and light, so they are exothermic. An example of a synthesis reaction is the formation of water from hydrogen and oxygen

An exothermic reaction is a chemical reaction in which less energy is needed to break bonds in the reactants than is released when new bonds form in the products. During an exothermic reaction, energy is constantly given off, often in the form of heat. All combustion reactions are exothermic reactions

Endothermic reactions are chemical reactions in which the reactants absorb heat energy from the surroundings to form products. These reactions lower the temperature of their surrounding area, thereby creating a cooling effect.

When we mix iron fillings with sulphur then we can separate it manually because they both are in solid form but in the case of the latter reaction we heat the mixture and it reacts with the atmosphere and forms a compound which can’t be reversed into its previous state. thus latter one is a chemical change.

A person eats a chocolate and then digests it, so there takes a chemical change because in the stomach digestion is held, the stomach adds special chemicals to digest it which when done is in-reversible. So, it is a chemical change because chemical changes are ir-reversible.

A chemical change is a change of materials into another, new materials with different properties and one or more than one new substances are formed. It results when a substance combines with another to form a new substance (synthesis or either decomposes to form more substances)