#9thclassonlinechemistry #chapter5 #Energetics Exothermic and Endothermic reactions

TEXT BOOK PAGE NUMBER: 71 and 72

Note: In this video the wordings are same as in the text book. Write Headings on your book. Notes are in description.

  5.3 Exothermic and Endothermic Reactions:

Part II

 

🔶 Exothermic Reactions in Daily Life

•        Our present-day living conditions depend heavily on the availability of energy in its various forms.

•        Exothermic chemical reactions are extensively used to fulfill this requirement.

•        In such reactions, chemical energy is converted into heat energy.

•        We burn fuels like gas, oil and coal to cook food and for other heating purposes in our homes and industry.

 

🔶 Combustion Process

• During this burning process called combustion, substances present in fuels react with oxygen of the air to produce a certain amount of heat.

 

🔶 Biological Fuels

•        Foods such as fats and carbohydrates are important biological fuels.

•        During metabolism, the chemical energy present in this food is converted to heat to keep us warm.

 

🔶 Electricity Production

•        A large portion of electricity is produced at power stations by burning fuels such as natural gas, oil and coal.

•        The heat which comes out from their combustion is used to produce steam at high pressure.

•        This high pressure steam is then used to rotate turbines, which in turn generate electricity.

 

🔶 Combustion in Vehicles

• While driving a vehicle, it is the combustion of petrol or diesel that gives off energy and drives it forward.

 

🔶 Fireworks - A Common Example

•        The one example of exothermic reactions people seem to enjoy the most is that of fireworks.

•        Fireworks are the result of combustion reactions that yield heat, light and sound.

•        Different metal salts along with oxidising agents produce a variety of colours when burnt, Fig. (5.2).

 

🔷 Fig (5.2) Fireworks

(Image showing colorful fireworks in the night sky)

 

🔷 Exercise Answers:

1.   Why the chemical reaction between sodium metal and water proceeds violently?

•        The reaction between sodium metal and water proceeds violently because it is a highly exothermic reaction. Sodium reacts with water to form sodium hydroxide and hydrogen gas, releasing a large amount of heat. This heat can ignite the hydrogen gas, causing flames or explosions.

2.   Is melting of ice an exothermic or endothermic change?

•        Melting of ice is an endothermic change because it absorbs heat from the surroundings to convert solid ice into liquid water.

3.   Can exothermic reaction be reversed?
Some exothermic reactions can be reversed under specific conditions, but not all. Generally, reversing an exothermic reaction requires input of energy, making the reverse process endothermic.

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