Transcript snc1d u2 lesson 4 physical and chemical properties 2

Physical and Chemical Properties
2
Lesson 4
September 27th, 2010
Temperature and Chemical
Change
• The application of heat to a substance can
cause chemical changes.
• If enough heat is applied to a combustible
material it will burst into flames.
Temperature and Chemical
Change
• Combustibility – The ability of a
substance to react quickly with oxygen to
produce light and heat.
• A reaction that gives off heat is known as an
exothermic reaction.
• Example: burning gasoline.
Temperature and Chemical
Change
• When some substances are
mixed and their reaction
absorbs heat, it is called an
endothermic reaction.
• Example: A chemical cold
pack.
Controlling Changes in Matter
to Meet Human Needs
Freezedrying
• A method of food preservation. (can last
from months to years)
• Food is frozen and then placed in a pressure
chamber where the pressure is reduced until the
solid water sublimes into gas.
Freezedrying
• 98% of the water is removed and once
packaged does not need to be refrigerated.
• To cook just add hot water
From Corn to Biodegradable
Plastic Wrap
• Chemicals made from corn can be used to
make juice bottles, remove paint or nail
polish, and fuel some cars.
From Corn to Biodegradable
Plastic Wrap
• Corn is put through a chemical change
called fermentation. Once this chemical
process is complete, the new substances are
recovered, purified, and made into solvents,
biodegradable plastics, and automobile fuel.
• Solvents are substances that dissolve other
substances.
• Corn-based solvents are not as harmful to the
environment as some other types of solvents.
From Corn to Biodegradable
Plastic Wrap
• An advantage of corn-based biodegradable
plastics is that they can be broken down by
bacteria.
• Corn-based products also have their
drawbacks.
• Rainforests have been cut to make corn
fields.
• Corn that would otherwise be used for food is
sometimes diverted to make disposable
products
Things to hand in
• Investigating Physical and Chemical
Changes
• You will write a quiz
• Study up