Physical and Chemical Changes

Physical Change

Physical changes occur when matter changes its property but not its chemical nature. The property could be its size, shape, state of matter, or color.

The key indicator of a physical change is that the identity of the substance remains the same.

• Physical changes could include a change in: texture, shape, size, color, odor, volume, mass, weight, and density.

• Examples of physical changes: cutting, stretching, grinding, folding and changes in states of matter.

Physical Change

Identity stays the same

A Change in the State of Matter is a Physical Change

• Melting- solid to liquid• Boiling/Evaporation- liquid to gas• Freezing- liquid to solid• Condensation- gas to liquid• Sublimation- solid to gas

Physical Changes

Some less obvious physical changes include:• Dissolving a substance• Conducting an electrical charge• Becoming magnetized

Chemical Change

Chemical changes are changesmatter undergoes when it becomesnew or different substance.

Chemical changes result in a substance changing its identity.

Chemical changes are also called

chemical reactions.

Signs of Chemical Reaction

• Signs of a chemical change includes: color change, bubbling and fizzing, light production, smoke, and presence of heat.

Chemical Changes Include:

• Burning• Rusting• Corrosion• Rotting or Decaying• Decomposition• Any kind of chemical reaction

• In a chemical change the atoms which make up the substances are not created or destroyed rather the bonds between them are broken and atoms rearrange forming new substances.

• Example

Exothermic and Endothermic Reactions• Exothermic reactions are reactions which

release heat. These reactions see an increase in temperature.

• Examples- An exothermic reaction in a Styrofoam cup will significantly raise the temperature in the cup.

• Endothermic reactions are reactions which absorb heat. These reactions see a decrease in temperature.

• Examples- • An endothermic reaction happens when the

temperature in a flask so that the flask will freeze and stick to a wet piece of wood. An endothermic reaction is used in drug store instant cold pack.

• When water is mixed with ammonium nitrate, the ammonium nitrate splits into ammonium and nitrate ions. Heat is absorbed and the temperature decreases. This is an example of an endothermic reaction.

• When propane gas is burned (combines with oxygen), carbon dioxide and water are produced and heat energy is produced. This is an example of an exothermic reaction.

Exothermic ReactionEnergy of the products are less than the energy of the reactants.

The energy is released as heat.

Activation energy is the energy needed to start the reaction.

Endothermic ReactionEnergy of the products is greater than the energy of the reactants.

Energy is absorbed by the reactants.

The Kinetic Molecular Theory

• All matter is made of atoms.• The atoms that make of matter are in constant,

random motion.• The speed of the particles is dependent on their

temperature. The warmer the matter, the faster the particles move.

• The 3 states of matter common on earth are solid, liquid, and gas.

• Solid has the least amount of energy while gases have the most amount.

The Kinetic Molecular Theory- Solids and Liquids

1. Solids are made of tiny particles that vibrate but cannot move past one another.

2. Solids have a fixed shape and fixed volume.3. Liquids are made of tiny particles close

together that can slide past one another.4. Liquids take up the shape of its container but

have a fixed amount. Liquids have an indefinite shape but a fixed volume.

The Kinetic Molecular Theory- Gases

1.Gases are made of tiny particles far apart relative to their size

2. Gas particles are in continuous, rapid, random motion.

3. Gas particles take up the entire size and shape of its container. Gases have an indefinite shape and volume.

4. The collisions of the gas particles on each other and the sides of its container cause pressure.

Energy and the States of Matter

1) In order to go from one state of matter to another, energy must be added or removed. The matter either absorbs or releases energy.

2) Let’s consider H2O. Ice absorbs energy in order to melt and become water. Water absorbs energy to become steam.

3) Conversely, water releases energy becoming ice and steam releases energy becoming water.

Heating Curve of Water- Friday’s Lab

• Freezing point/melting point of H2O is 0 C or 32 F

• Boiling point/point of condensation of H2O is 100 C or 212 F

• A water/ice combo will stay at 0 C until all the ice melt then it will rise.

• Boiling water will stay at 100 C until all of it boils. Steam can go hotter than 100 C.