Chemical Reactions and Their Indicators

The video explains chemical reactions as processes that result in chemical changes, forming new substances with different properties. It provides examples like burning fuel, digestion, and respiration. The video also describes how to identify chemical reactions through changes in state, temperature, gas evolution, color change, and precipitate formation. Experiments with zinc and sulfuric acid, potassium iodide and lead nitrate, and copper sulphate and zinc demonstrate these concepts.

What is a chemical reaction?

• A process where substances retain their original properties

• A process where new substances with new properties are formed

• A process that involves only physical changes

• A process that does not involve any change in substances

Which of the following is an example of a chemical reaction?

• Melting of ice

• Freezing of water

• Burning of fuel

• Boiling of water

What observable change indicates a chemical reaction?

• Change in size

• Change in state

• Change in texture

• Change in shape

What happens when zinc reacts with sulfuric acid?

• No change occurs

• A solid is formed

• Gas is evolved and temperature increases

• The solution becomes cold

What does the evolution of gas in a reaction indicate?

• A physical change

• A chemical reaction is taking place

• No reaction is occurring

• The substances are dissolving

What is formed when potassium iodide reacts with lead nitrate?

• A gas

• A precipitate

• A colorless solution

• A solid metal

What does the formation of a precipitate indicate?

• A chemical reaction

• A temperature change

• A physical change

• No change

What change is observed when zinc is added to copper sulfate?

• The solution remains blue

• A precipitate is formed

• A gas is evolved

• The solution becomes colorless

What does a change in color during a reaction signify?

• A temperature change

• A physical change

• A chemical reaction

• No change

Which of the following is NOT a characteristic of a chemical reaction?

• Evolution of gas

• Change in texture

• Change in temperature

• Change in state