Pressure/Introductory Thermodynamics

In summary, the conversation discusses a chemical reaction taking place in a container with a cross-sectional area of 100 cm2. As a result, a piston is pushed out 20 cm against an external pressure of 567 torr. The conversation then asks for the value of w for this reaction, with the reminder that the sign matters. The solution is shown, but it is noted that the sign was initially disregarded, leading to an incorrect answer.
  • #1
JamesL
33
0
Not sure what I am doing wrong...

Homework Statement


A chemical reaction takes place in a container
of cross-sectional area 100 cm2. As a result of
the reaction, a piston is pushed out through 20
cm against an external pressure of 567 torr.
What is the value for w for this reaction?
(Sign does matter.) Answer in units of J.

Homework Equations



w = - (Pressure)(Change in Volume)


The Attempt at a Solution



Cross sectional area = 100 cm^2 = .01 m^2
Change is piston distance = 20cm = .2 m

Pressure = 567 torr x 133.322 = 75593.574 Pa


Solution disregarding sign = [75593.574 kg/(m*s^2)][.01 m^2][.2 m]

---> 151.188 J

However this is coming up as incorrect.
 
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  • #2
Looks OK to me. Why are you ignoring the sign when it says "sign does matter"?
 
  • #3
Doc Al said:
Looks OK to me. Why are you ignoring the sign when it says "sign does matter"?

This is why a separate set of eyes is always helpful!
 

1. What is pressure?

Pressure is defined as the force per unit area applied on a surface. It is a measure of how much force is exerted on a given area.

2. How is pressure measured?

Pressure is typically measured using a device called a manometer, which uses a column of liquid to determine the difference in pressure between two points. It can also be measured using instruments such as barometers or pressure gauges.

3. What is the relationship between pressure and temperature?

According to the Ideal Gas Law, pressure and temperature have a direct relationship. As temperature increases, so does the pressure, and vice versa. This is because as the temperature of a gas increases, the particles in the gas move faster and collide with the walls of the container more frequently, resulting in an increase in pressure.

4. How does pressure affect the boiling point of a substance?

As pressure increases, the boiling point of a substance also increases. This is because at higher pressures, it takes more energy for the molecules of the substance to escape the liquid phase and turn into a gas. This is why water boils at a higher temperature at higher altitudes where the atmospheric pressure is lower.

5. What is the difference between absolute and gauge pressure?

Absolute pressure is the total pressure exerted on a surface, including atmospheric pressure. Gauge pressure, on the other hand, only measures the pressure above atmospheric pressure. This means that absolute pressure will always be higher than gauge pressure, since it includes the pressure of the surrounding atmosphere.

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