Physical and Chemical Changes

Lesson 1: Physical or Chemical Change Vocabulary

• Reversible: Capable of being reversed
• Irreversible: Not capable of being reversed
• Physical change: A change that alters the form or appearance of a substance but does not change it into a new substance
• Chemical change: A change that produces a new substance
• Matter: Anything that has mass and takes up space
• Particle: A minute portion of matter
• Arrange: To place in a particular order
• Rearrange: To change the order or position of something

Matter and Changes

• Matter exists everywhere
• Changes in matter occur constantly

Reversible vs. Irreversible Changes

• Reversible change: Alters a substance's shape or size without changing its characteristics
• Irreversible change: Results in a new substance

Chemical vs. Physical Changes

• Chemical change: Results in new substances and is usually irreversible
• Physical change: Does not produce new substances

Examples of Physical and Chemical Changes

• Physical changes include chocolate melting, wax melting, sugar dissolving, water boiling, puddle evaporating, water condensing, butter melting, ice melting, oil and water mixing
• Chemical changes include bread toasting, candle burning, wood burning, biscuits baking, potatoes boiling, cakes baking

Signs of Chemical Change

• Bubbles are formed
• Color changes occur
• A solid is formed
• Light and heat are produced
• A sweet or foul smell is present
• Loud explosion happens

States of Matter

• Matter exists in three states: solid, liquid, and gas

Arrangement of Particles in Solids

• Particles in a solid are closely packed together
• They are arranged in a fixed pattern
• They vibrate in place

Arrangement of Particles in Liquids

• Particles in a liquid are closely packed
• They can move about and slide past each other

Arrangement of Particles in Gases

• Particles in a gas are far apart
• They move about very quickly

Physical Changes at a Particle Level

• The arrangement of particles changes, but the particles themselves remain the same

Chemical Changes at a Particle Level

• Particles rearrange to form new substances

Conservation of Mass in Chemical Changes

• The mass of the substance does not change before and after the reaction

Lesson 2: Changes Around Us Vocabulary

• Oxygen
• Carbon dioxide
• Swallow
• Chew

Detecting Exhaled Gas

• Clear lime water tests for the presence of exhaled gases

Reaction of Carbon Dioxide with Lime Water

• Carbon dioxide gas makes clear lime water cloudy
• This is a chemical change

Gases Exchanged by Humans

• Inhale oxygen
• Exhale carbon dioxide
• Gas exchange in our bodies represents a chemical change

Digestive System

• Mouth, esophagus, stomach, large intestines, small intestines all digest food

Starch, Bread, and Iodine

• Starch in bread turns iodine blue
• Breaking bread via chewing is a physical change

Enzymes and Bread

• Enzymes in saliva react with the starch in bread
• This is a chemical change
• Chewed bread no longer discolors iodine

Digestion in the Stomach

• Stomach muscles mix food with acids and enzymes
• Acids and gastric juices break down food into absorbable liquids
• This process involves chemical changes

Knowledge Extension: Chemical Reactions

• Mixing baking soda and white vinegar produces carbon dioxide gas
• Carbon dioxide is a colorless, odorless gas, heavier than air, non-combustible, and can extinguish fires

Physical Change: Dry Ice

• Carbon dioxide gas turning into dry ice is a physical change
• Carbon dioxide is used for artificial rain, food refrigeration, carbonated drinks, and fire extinguishers

The Transformation of Sugar

• Heating white sugar creates a new substance
• Sugar melts, representing a physical change
• Melted sugar turns yellow, then darkens, becoming a black solid that emits smoke with a particular scent
• The resulting black solid and scent both qualify as new substances
• Therefore, heating white sugar results in a chemical change

Burning Candle Wax

• Burning candle wax creates new substances
• Placing a clear glass over a candle flame reveals water droplets on the glass
• Briefly holding a glass slide to a candle flame will leave black carbon residue
• Burning candle wax produces new substances, and therefore means it is a chemical change

Fireworks Composition and Reaction

• Fireworks consist mainly of gunpowder
• Burning gunpowder produces new substances like gases
• Reaction emits light and heat, marking it a chemical change

Corrosion of Copper Lions

• Copper lions are cast from bronze alloys
• Green coatings on the surface indicate a change where new green substances are created
• This marks it as a chemical change

Rusting of Iron

• Iron rusts upon prolonged exposure to oxygen and moisture in the air
• Rust is a reddish-brown substance, less durable and easier to erode than iron
• A completely rusted piece of iron can expand in volume by eight times
• Failure to remove rust accelerates corrosion, as it easily absorbs moisture

Preventing Rust

• Preventing rust involves blocking the iron from contacting water and air
• Traditional rust prevention methods include: applying paint, electroplating, creating alloys, greasing, enameling, keeping dry, forming an oxide film, etc.

Examples of Chemical Changes

• Baking cakes using flour and cooking shrimp until red both generate new substances, and are chemical changes

The Chemistry of Baking

• Yeast converts starch into alcohol and carbon dioxide, along with sugar amino acids, organic acids, and lipids
• Lipids give dough its aroma, while carbon dioxide makes the dough porous, fluffy and pliant

The Chemistry of Cooking Shrimp

• Shrimp turns red due to astaxanthin
• Astaxanthin can combine with different forms of protein, and change to other colors
• When protein is damaged, denatured or separated, the color reverts to the original orange-red hue

Helpful and Harmful Chemical Changes

• Beneficial chemical changes: grain fermentation, metal smelting, etc
• Harmful chemical changes: iron rusting, acid rain damaging forests and corroding buildings, etc

Phenomena Accompanying Chemical Changes

• Phenomena: color change (iron rusting), light and heat emission (candle burning), gas production (mixing vinegar and baking soda), precipitate production (mixing milk and vinegar), etc
• Sometimes, these phenomena happen simultaneously

Physical Changes

• Not all color, light, heat, gas, or precipitate-related changes involve new substances
• These examples relate to physical change: light bulb emitting light, sediment settling, water boiling, ink dilution