1. QUESTION:
A person with a fever (38oC) is given an alcohol rub. As the alcohol evaporates, the algebraic sign for q for the alcohol is ________ and q for the person is ________. A. positive, positive, B. positive, negative C. negative, positive, D. negative, negative
Vaporization is an endothermic process. This means that heat flows into the a liquid as it is transformed into a gas.
By convention, q is assigned a positive value for an endothermic process; and q is assigned a negative value for an exothermic process.
Consider the following….
A person with a fever (38oC) is given an alcohol rub. As the alcohol evaporates, the algebraic sign for q for the alcohol is ________ and q for the person is ________. Fill in the blanks with the words positive or negative.
PAUSE CLICK Vaporization is an endothermic process. This means that heat flows into the a liquid as it is transformed into a gas.
In the transformation molecules spread out…. In order for molecules to move farther apart, they need energy to be able to overcome
the forces that are holding them together in a liquid. The alcohol molecules that go into the gas phase gain this energy through
random collisions with neighboring molecules, including the molecules in the person’s body.
CLICK
As a matter of convention, the amount of heat flow,…q
HIGHLIGHT q
is assigned a positive value for an endothermic process.
HIGHLIGHT positive and endothermic
Therefore, the algebraic sign for the alcohol is positive.
FILL IN THE BLANK WITH “positive”
The heat that flowed into the alcohol came from the person’s body.
So, we say that there is heat flow OUT of the person. The outflow of heat is what we would call an exothermic process.
HIGHLIGHT exothermic
and, by convention, the value of q is assigned a negative value for an exothermic process.
HIGHLIGHT negative
Since alcohol evaporates rapidly, this explains how an alcohol rub can be useful in quickly reducing the temperature of someone with a fever.
CLICK PAUSE END RECORDING

2. Video ID: © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Assisted by Johuan Gasery In partial fulfillment of the requirements for CHEM 481, Fall 2008.