Phase+Changes--by+AnnYU

(Text.P59-61)
There are generally two big types of substance change: they are **CHEMICAL CHANGE** & **PHYSICAL CHANGE**.

CHEMICAL CHANGE -- a change when __new substances__ are formed. ( Text. P59 ) PHYSICAL CHANGE -- a change in the PHASE of a substances, such that __NO new substances__ are formed. ( Text. P59 )

Here, we mainly talk about PHYSICAL CHANGE.

Matters have three different PHASES -- LIQUID, SOLID, GAS.


 * LIQUID** **PHASE**
 * http://farm4.static.flickr.com/3011/2295623086_77d3658532.jpg


 * SOLID PHASE**
 * http://www.mii.org/Minerals/Minpics1/CoalBituminous.jpg


 * GAS PHASE**
 * http://helloworldbea.files.wordpress.com/2008/05/watervapor.jpg

Let's use the substance water (H2O) as an example to explore the **change in TEMPERATURE** during phase changes. Solid >> Liquid >> Gas Ice >> Water >> Steam


 * http://universe-review.ca/I12-20-phasechange.jpg

**Key Terms Definitions (Textbook P60):**
__**Freezing Temperature**__: is the temperature at which a liquid changes into the solid phase.(same as melting temperature) __**Boiling Temperature**__: is the temperature at which a liquid changes into the gas phase.(In the above graph, the temperature of points d&e)
 * __Melting Temperature__**: is the temperature at which a solid changes into the liquid phase.(In the above graph, the temperature of points b&c)
 * At the **MELTING/FREEZING** temperature the solid and liquid phases co-exist.
 * __Condensation Temperature__**: is the temperature at which a gas phase changes into the liquid phase.(same as boiling temperature)
 * At the **BOILING/CONDENSING** temperature the liquid and gas phases co-exist

The below image demonstrates vividly how the molecules of a substance move and react as the heat enery increases during phase changes. This image also helps people to be familiar with the terms used to describe phase changes.
 * http://www-bioc.rice.edu/pblclass/6th%20grade/Geology/phase.bmp

__**Analyzing the Above Graph:**__
all the heat energy that enters the system is used to warm the substances, so the temperature increases.
 * On the sloping portions of the graph (line segments with slopes):**

the substance cannot contain so much heat energy, and it stays in the same temperature. Heat is used to break up the bonds and lengthen the distance between molecules and allow solid form turns into liquid form or liquid form turns into gas form.
 * On the level portions of the graph (horizontal line segments):**

Energy Involved in Chemical and Physical Changes:


The amount of heat involved in a physical change is __**much less than**__ the amount involved in a chemical change.

Quiz Time!
Do some research on the internet about gold (Au).
 * []

1.What's solid gold's melting temperature?

2.What's liquild gold's boiling temperature?

3.Describe the movement of the gold molecules and the change of the temperature:

-- when the gold is melting

-- when the gold is boiling.

Answer Key!
1. 1064 Celsius 2. 2856 Celsius 3. -- During the melting period, the temperature remains at 1064 Celsius, and the solid gold molecules absorb heat energy to loosen their tight bonds gradually and move away from each other farther and farther to get into the positions of liquid gold molecules. -- During the boiling period, the temperature reamains at 2856 Celsius, and the liquid gold molecules absorb heat energy to move more apart from each other to get into the positions of gas gold molecules.