Question

1. which everyday activity involves a chemical change?

a) tearing paper
b) baking a cake
c) melting butter
d) breaking glass

1. which of the following shows conservation of matter?

a) total mass of reactants equals total mass of products
b) mass increases after a reaction
c) mass decreases after a reaction
d) mass disappears after burning

1. which observation best shows an exothermic reaction?

a) the container becomes hot
b) the solution absorbs heat
c) color of solution fades
d) ice cube melts

Explanation:

🆕 New Concept Discovered: Chemical vs. Physical Changes
New substances form during chemical changes.

🆕 New Concept Discovered: Conservation of Matter
Matter cannot be created or destroyed.

🆕 New Concept Discovered: Exothermic vs. Endothermic
Exothermic reactions release heat to their surroundings.

Step 1: Analyze Question 12 (Chemical vs. Physical Changes)

A physical change alters the form or appearance of a substance without changing its chemical identity (e.g., tearing, breaking, or changing state like melting). A chemical change occurs when substances react to form entirely new substances with different chemical properties.

• A) Tearing paper: Only changes the size and shape (physical change).
• B) Baking a cake: Heat causes chemical reactions between ingredients (like baking powder reacting to release gas, and proteins/sugars bonding), creating a new substance that cannot be easily reversed (chemical change).
• C) Melting butter: A change of state from solid to liquid (physical change).
• D) Breaking glass: Only changes the shape and size (physical change).

Therefore, the correct option is B.

Step 2: Analyze Question 13 (Conservation of Matter)

The Law of Conservation of Mass (or Matter) states that in a closed system, matter cannot be created or destroyed during a chemical reaction.

• This means the total mass of the starting materials (reactants) must be exactly equal to the total mass of the resulting substances (products).

Therefore, the correct option is A.

Step 3: Analyze Question 14 (Exothermic vs. Endothermic)

An exothermic reaction is a chemical process that releases energy in the form of heat to its surroundings.

• When heat is released into the surroundings, the temperature of the reaction container rises, making it feel hot to the touch.
• Absorbing heat (option B) and melting ice (option D) are endothermic processes (they absorb heat from the surroundings).

Therefore, the correct option is A.

Answer:

• 12: B) Baking a cake
• 13: A) Total mass of reactants equals total mass of products
• 14: A) The container becomes hot