States of Matter

The 4 States of Matter Solid Liquid Gas Plasma

Solids - Have definite volume - Have definite shape - Molecules are held in specific locations - By electrical forces - Vibrate about equilibrium positions - Can be modeled as springs connecting molecules

Solids External forces can be applied to the solid and compress the material - In the model, the springs would be compressed When the force is removed, the solid returns to its original shape and size - This property is called elasticity

Crystalline Solids Atoms have an ordered structure - This example is salt Gray spheres represent Na+ ions Green spheres represent Cl- ions

Amorphous Solids Atoms are arranged almost randomly Examples include glass

Liquids - Has a definite volume - No definite shape - Exists at a higher temperature than solids - The molecules “wander” through the liquid in a random fashion - The intermolecular forces are not strong enough to keep the molecules in a fixed position

Gases - Has no definite volume - Has no definite shape - Molecules are in constant random motion - The molecules exert only weak forces on each other - Average distance between molecules is large compared to the size of the molecules

Gases - Gas heated to a very high temperature - Many of the electrons are freed from the nucleus - Result is a collection of free, electrically charged ions - Plasmas exist inside stars

Deformation of Solids - All objects are deformable - It is possible to change the shape or size (or both) of an object through the application of external forces - When the forces are removed, the object tends to return to its original shape - An object undergoing this type of deformation exhibits elastic behavior

Elastic Properties - Stress is the force per unit area causing the deformation - Strain is a measure of the amount of deformation

Changes of State The melting point of a material is the temperature at which solid material begins to shed its molecular bonds and melt into a liquid. (And is also the freezing point, where molecules bond together more structurally to form a solid.) The boiling point is the temperature at which a liquid completely breaks free and becomes a gas (Also the point of condensation for gases back into liquids.)

Changes of State

What happens during those ‘flat’ periods? As matter is changing from one phase to another, the temperature does not change due to one of two factors: When heating materials, the added energy is being absorbed to break the molecular bonds within the material as it transition from one state to another. When cooling materials, as molecular bonds are being formed, thermal energy is being produced in the process, keeping the temperature steady until the state change is complete.

Heat of Fusion When heating a solid material, when its temperature reaches its melting point, a certain amount of heat is required to fully convert that solid into liquid. This amount of heat is called heat of fusion and it differs for every type of material. Heat of fusion is the amount of thermal energy needed to melt 1 kg of a substance.

Heat of Vaporization Similarly, when heating a liquid material, when its temperature reaches its boiling point, a certain amount of heat is required to fully convert that liquid into a gas. This amount of heat is called heat of vaporization, and again, it also differs for every type of material. Heat of vaporization is the amount of thermal energy needed to vaporize 1 kg of a substance.

State Change Heat Both heat of fusion (Hf) and heat of vaporization (Hv) are measured in J/kg Heat required to melt a solid: Q = m Hf Heat required to vaporize a liquid: Q = m Hv

State Change Heat

State Change Problem A 27kg block of aluminum is heated to its melting point of 660°C. How much additional heat will be needed to fully melt the aluminum down? (Hf of aluminum = 3.97 x 105 J/kg)

State Change Problem This now 27kg puddle of molten aluminum is further heated until it reaches its boiling point of 2450°C. How much additional heat will be needed to fully vaporize the aluminum? (Hv of aluminum = 1.14 x 107 J/kg)

Total Heat Problem Suppose we start with a 3kg block of water ice with a temperature of -5°C. Adding heat to the ice, we eventually melt it down, then bring it to a boil, and eventually the temperature of the steam it forms ends up being 120°C. How much total heat was added in this entire process? Specific heat of water: 4181 J/kgK Heat of fusion of water: 3.33 x 105 J/kg Heat of vaporization of water: 2.26 x 106 J/kg