# Thermodynamics - Change in volume

• janiexo
In summary, the Golden Great Bridge on planet Tehar experiences a change in length due to temperature fluctuations, with the bridge being a long slab of pure gold. The bridge-building technology on Tehar is not very well developed, and the bridge's length is affected by the air temperature. The bridge experiences a 4% increase in volume between the winter and summer, using the formula L = L_0 (1 + \alpha \Delta T) and ignoring terms with higher powers of \alpha.
janiexo
The next few questions refer to the Golden Great Bridge, built on planet Tehar in a galaxy far, far away. The bridge-building technology on Tehar is not very well developed: The bridge is just a long slab of pure gold with the opposite ends resting on the shores of the river.

In the spring, when the air temperature is 100 degrees Celsius, the length of the bridge is 160.0 klops (the klop is the unit of length on Tehar). Answer the questions below knowing that the value of alpha for gold is 1.4*10^-5.

Temperature in Winter: -150 degrees celcius
Temperature in Summer: 700 degrees celcius

By what percentage does the volume of the bridge increase between the winter and the summer?

I don't really know how to go about doing this question because it doesn't give the initial volume of the bridge. I tried to write 2 equations, one for the change in volume between winter and spring and another for the change in volume between spring and summer. I then canceled out the volume in spring in both equations and rearranged the combined equation to get volume in summer/volume in winter and got an answer of 1.04 which i * by 100 to get 104%, which was wrong. What is the proper way I'm meant to approach this question because that is the only way I can see to do it.

hi janiexo

the question is wrong i guess...because u have mentioned that bridge is just a long slab...so here there is no usa of talking abt its volume change throughout the year...the variation in length maybe a useful matter to discuss here...i think so...

nomorevishnu said:
hi janiexo

the question is wrong i guess...because u have mentioned that bridge is just a long slab...so here there is no usa of talking abt its volume change throughout the year...the variation in length maybe a useful matter to discuss here...i think so...

The two questions before it were related to length:
*By what amount (deltaL) does the length of the bridge decrease during the Teharian winter when the temperature hovers around -150 degrees celcius
* By what amount does the length of the bridge increase during the Teharian summer when the temperature hovers around 700 degrees celcius?

I got them without too much problem, but the volume question is another matter :(

You can find by what percentage the length changes, without knowing the length using $L = L_0 (1 + \alpha \Delta T)$.

Do the same thing for the volume (which is $L^3$), realizing that since $\alpha$ is small you can ignore terms with higher powers of $\alpha$.

I must not have understood because I got the same answer of 104%... or should it be 4% maybe? It says to "Express your answer as a percentage. Use three significant figures."

104 versus 4 = big difference! The percentage increase in volume is only about 4 percent, not 104!

Kind of strange to calculate the percentage change to 3 sig figs, when alpha is only given to 2 sig figs.

Haha yep it was around 4%... I can't believe I did all of the hard work and didn't even know whether it should be 104% or 4%. Thanks for your help :)

## 1. What is the definition of "change in volume" in thermodynamics?

In thermodynamics, "change in volume" refers to the difference in the amount of space occupied by a substance before and after a physical or chemical process.

## 2. How is the change in volume related to the first law of thermodynamics?

The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or converted. In the context of change in volume, this means that the energy input or output of a system can cause a change in volume through work or heat transfer.

## 3. Can the change in volume of a system be negative?

Yes, the change in volume can be negative if the system undergoes a decrease in volume due to external factors such as compression or cooling.

## 4. How is the change in volume related to the ideal gas law?

The ideal gas law, PV = nRT, relates the pressure, volume, amount of gas, and temperature of an ideal gas. It can be used to calculate the change in volume of a gas when other variables are known, such as pressure, temperature, and number of moles.

## 5. What factors can cause a change in volume in a system?

Some factors that can cause a change in volume in a system include temperature changes, changes in pressure, chemical reactions, and external forces such as compression or expansion.

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