Physical and Chemical Changes

What is a physical change?

A change in which now new substances are formed.

What are some examples of physical changes?

Changes of state (melting, freezing, evaporation), mixing, and dissolving.

In a physical change, what happens to the molecules?

The same molecules are present before and after; they are just rearranged or moved.

What is a chemical change?

A change is which new substances are formed.

What happens to atoms in a chemical change?

The atoms are rearranged to form new particles (substances).

What are some examples of chemical changes?

Rusting, burning, cooking food. and photosynthesis.

What evidence shows a chemical reaction has taken place?

Temperature change, color change, gas formation, or formation of a precipitate.

How do you test for oxygen?

Insert a glowing splint-if it relights, oxygen is present.

How do you test for hydrogen?

Place a lit splint near the gas-if you hear a ‘pop’ sound, hydrogen is present.

How do you test for carbon dioxide?

Bubble the gas through limewater-if it turns milky, carbon dioxide is present.

What is the main difference between physical and chemical changes?

Physical changes do not form new substances, while chemical changes do.

What are reactants and products?

Reactants are the starting substances; products are the new substances formed.

What is the law of coservation of matter?

Matter is neither created nor destroyed in a reaction; atoms are simply rearranged.

Example: Write a word equation for iron rusting.

Iron + Oxygen - Iron oxide

What are some important examples of chemical reactions?

Photosynthesis, respiration, and chemical weathering.

Write a word equation for photosynthesis.

Carbon dioxide + Water - Glucose + Oxygen (with light energy)

Write the word equation for respiration.

Glucose + Oxygen - Carbon dioxide + Water + Energy

Name some common acids found at home.

Vinegar, lemon juice, and battery acid.

Name some common bases found at home.

Caustic soda, ammonia, baking soda.

What are the properties of acids?

Sour taste, some are corrosive.

What are the properties of bases?

Bitter taste, slippery feel, some are corrosive.

Name some common laboratory acids.

Hydrochloric acid, sulfuric acid, nitric acid, acetic acid, citric acid, carbonic acid

Name some common laboratory bases.

Sodium hydroxide, calcium hydroxide, ammonia, sodium bicorbonate.

What is an indicator?

A chemical that changes color depending on whether it’s in an acidic or basic solution.

Name two common indicators used in labs,

Litmus and Universal Indicator.

What color does litmus turn in acid and base?

Red in acid, blue in base.

How can indicators determine acidity or basicity?

By color changes that correspond to the pH value.

What is the pH scale?

A scale that classifies substances as acidic, basic, or neutral.

What pH values correspond to acids, bases, and neutral substances?

Acids: less than 7, Neutral: 7, Bases: greater than 7.