Chemistry Reference
In-Depth Information
3.
_______________ is the process of a solid changing directly to a gas,
without passing through the liquid phase.
4.
_______________ changes do not result in the production of new
substances.
5. Melting is an example of a change-of- _______________ operation.
6. Which of the following is not an example of a physical change?
a) breaking glass c) cutting wood
b) melting gold d) burning wood
7. Which of the following represents matter in a solid form?
a) CO
2(g)
b) H
2
O
(s)
c) CCl
4(l)
d) O
2(g)
8. Which of the following correctly represents the process of
sublimation?
a) CO
2(g)
CO
2(s)
c) CO
2(g)
CO
2(l)
b) CO
2(s)
CO
2(g)
d) CO
2(l)
CO
2(s)
9. Explain how physical changes differ from chemical changes.
10. Does dissolving sugar in water represent a physical change or a
chemical change? Explain your answer.
Lesson 1-5: Energy and Chemical Reactions
In the last lesson you read about the Law of Conservation of Mass.
Energy has its own conservation law, appropriately called the Law of Conser-
vation of Energy. This law states that the total amount of energy in the uni-
verse is conserved. In other words, energy is not created or destroyed; it only
changes form. Einstein combined these two conservation laws into the Law
of Conservation of Mass-Energy, with his formula E=mc
2
, to illustrate what
happens in a nuclear reaction. When dealing with only physical and chemi-
cal changes, as we are now, we apply the original conservation laws.
Let's suppose a bowling ball fell off a shelf and landed on your foot,
breaking one of your toes. When the bowling ball hit your foot, it trans-
ferred energy into it. Where did the bowling ball get the energy in the first
place? It certainly didn't create it. The person who put the bowling ball on
the shelf did work lifting it up, transferring energy into it, and the bowling
ball stored that energy as potential energy.
Energy is often defined as the ability to do work. Work, in this case, is
defined as a force exerted over a distance. Energy, then, is the ability to
