Phase Changes/Heating Cooling Curves

Blog Post #2

(April 26, 2016)

Our last lecture of this unit presented us with two different types of graphs:

Heating and Cooling Curve: Shows where an element/compound will freeze/boil/melt.

Add caption

http://www.kentchemistry.com/images/links/matter/HeatCool.gif


Things to Know about Heating/Cooling:

• change of state is a physical change    
• melting and boiling points are determined by the vapor pressures of the solid and liquid states
• at 0 degrees Celsius, ice and liquid water have the same vapor pressure.
• at 100 degrees Celsius, water vapor and atm are equal.

Phase Diagram: A representation of the states of a substance in relation to temperature and pressure.

http://d2vlcm61l7u1fs.cloudfront.net/media%2F654%2F654abc63-5ebf-4f33-9507-c38acd719f38%2FphpAsNMSr.png

Things to Know about Phase Diagrams:

• triple point-point at which the solid, liquid, and vapor states all have the same vapor pressure and coexist.
• critical temperature-the temperature above which the vapor cannot be liquefied, regardless of the pressure applied.
• critical pressure-the pressure required to liquefy the vapor at the critical temperature
• critical point-point at which the critical temperature and critical pressure coincide

Useful Links:

Heating and Cooling Curves

Heating Curves

Crash Course-Enthalpy

Measuring Energy Changes

Blog Post #1
Earlier this week, we had started a new unit over Energy and Phase Changes.
Energy changes accompany all chemical reactions and are due to the rearranging of chemical bonds. In fact, addition of energy is always a requirement for the breaking of bonds, but the breaking of bonds in itself, does not release energy. 
Chemists define work as directed energy change resulting from a process.

There are many different types of energy:
Kinetic Energy- energy of motion
Radiant Energy- Energy from the sun or solar energy
Thermal Energy-Energy associated with the random motion of atoms and molecules
Chemical Energy- Energy stored within the structural units of chemical substances
Potential Energy- Energy stored or energy of position

http://mskuksclass.weebly.com/uploads/1/9/7/1/19719395/8207568_orig.jpg

In calculating heat, we typically use the formula Q=mcAt
Q=heat in joules
M=mass in grams
c=specific heat in (J/g degree C)
AT=Change in temperature
https://s-media-cache-ak0.pinimg.com/736x/cd/80/5e/cd805e4fe12071be7b4a7ce04fac0709.jpg

Useful Links:
How To Determine Specific Heat
Measuring the Quantity of Heat