Changes in Chemistry

Physical and Chemical Changes

Physical Change

The characteristics of a substance or its physical properties are changed in some way but no new chemical substance is formed. It is usually reversible. The arrangements of particles do not change.

Chemical Change

When one or more substances under go a chemical reaction and a new substance is formed. Usually irreversible. The particles arrangement of particles changes creating new bonds and breaking old ones.

A chemical change occurs when..

Permanent Colour Change

Light and Sound is Produced

Change in temperature

Precipitate if formed

Gas is formed

A physical change occurs when..

Non-permanent colour change

When substances are mixed/dissolved in another substance

Change in shape

Expansion/Contraction

Change in state of matter

non-permanent colour change examples

Metal glowing red when heated

Mixing and dissolving examples

Sugar dissolving in water

Change in shape example

Ice melting into water and evaporating into water vapour

Expansion and Contraction Example

A balloon getting bigger in hotter air temperatures and smaller in colder air temperatures

Change in shape example

Smashing glass

Light and Sound examples

Fireworks, Frying eggs and Burning wood and fire

Change in temperature examples

Burning wood- wood reacts with oxygen. heat and light are released. Temperature increases.

Precipitate is formed examples

Curled milk- Acid in the milk causes milk proteins to stick together. The proteins form lumps. these lumps are called precipitates.

Gas is formed examples

Baking bread- yeast is added in produces carbon dioxide that expands inside the dough creating gas bubbles and causing bread to rise

Permanent Colour Change examples

Bannans going from green to yellow to brown- ripening and rotting

Toasting marshmallows- White to brown

What side do reactants go on

Left

What side do the products go on

Right

Exothermic Reaction

a chemical or physical reaction that releases energy, usually as heat, into its surroundings.

Examples of Exothermic Reactions

Combustion- Burning fuels release heat and light

Oxidiation-Rusting iron slowly releases energy over time

Lighting a candle

Nuclear Reactions

Endothermic Reactions

process or reaction absorbs heat from its surroundings, causing the system to gain energy while the surroundings feel cooler.

Examples of Endothermic Reactions

Melting Ice- Heat is absorbed to change ice to water

Photosynthesis- Plants absorb sunlight

Chemical Cold ice packs- absorb heat from skin and surroundings

Chemical Reactions Products and Reactants

During a chemical reaction, the bonds in reactants molecules are broken and the atoms rearrange to form new bonds creating the products.

Difference between Physical and Chemical Changes

Physical change no new substance is formed whilst chemical change a new substance is formed. Chemical change bonds break and new ones are formed whilst physical change the molecule structure stays the same.