1cal <===== 4.18J , efficiency?

[alpha2cen]

We know this conversion factor well. Then, is the efficiency about 100%? How do we prove it?

Edited January 25, 2011 by alpha2cen

[Fuzzwood]

Well it takes 4.18 J to heat 1 g of water by 1 °C. That is sort of the definition of 1 cal

[swansont]

Efficiency doesn't enter into it. It's a conversion factor.

[alpha2cen]

Is real molecular energy 5^oC water 1g - 4^oC water 1g 4.18J?

E( 5^oC water 1g) - E(4^oC water 1g) = 4.18J ??

Edited January 25, 2011 by alpha2cen

[Fuzzwood]

Indeed, cooling water down by 1 °C requires the environment to take up 4.18 J of energy. q = mass x specific heat x deltaT

Edited January 25, 2011 by Fuzzwood

[Sisyphus]

The calorie and the joule (as well as the BTU, foot pound, electron volt, and kilowatt hour) are both measures of the same thing, energy, much like feet and meters are both measures of distance. Nothing physically changes as a result of what units you choose to use, so there is no efficiency to consider.

 

As for the second question: because of how Celsius is now defined, the difference in energy between one gram of liquid water at one temperature and one gram of liquid water +/- one degree Celsius is not entirely constant, and depends on the starting temperature of the water. It is approximately one calorie (or 4.184 joules), but can be slightly more or less.

[alpha2cen]

The calorie and the joule (as well as the BTU, foot pound, electron volt, and kilowatt hour) are both measures of the same thing, energy, much like feet and meters are both measures of distance. Nothing physically changes as a result of what units you choose to use, so there is no efficiency to consider.

 

As for the second question: because of how Celsius is now defined, the difference in energy between one gram of liquid water at one temperature and one gram of liquid water +/- one degree Celsius is not entirely constant, and depends on the starting temperature of the water. It is approximately one calorie (or 4.184 joules), but can be slightly more or less.

 

Total energy difference 5^oCwater 1g minus 4^oCwater 1g is 1cal from cal definition.

But, is statistical mechanical total energy difference 5^oCwater 1g minus 4^oCwater 1g is 4.184J?

Work energy 4.184J ---------> 1cal yes

Heat energy 1cal -------------> 4.184J ??

Edited January 26, 2011 by alpha2cen

[Sisyphus]

Total energy difference 5^oCwater 1g minus 4^oCwater 1g is 1cal from cal definition.

 

Actually, no, it isn't. It is approximately 1 calorie. The energy needed to raise the temperature of water is not entirely constant.

 

But, is statistical mechanical total energy difference 5^oCwater 1g minus 4^oCwater 1g is 4.184J?

Work energy 4.184J ---------> 1cal yes

Heat energy 1cal -------------> 4.184J ??

 

Joules and calories are not measures of "work energy" and "heat energy." They are measures of energy. The same thing.

[alpha2cen]

 

Joules and calories are not measures of "work energy" and "heat energy." They are measures of energy. The same thing.

 

But experimentally 1cal =4.184jule means mechanical energy -----> heat energy.

Is this wrong?

[swansont]

But experimentally 1cal =4.184jule means mechanical energy -----> heat energy.

Is this wrong?

 

It's wrong; it applies to any form of energy, as Sisyphus has already explained.

[alpha2cen]

The transform heat energy to mechanical is not proved.

It is not easy from heat energy to mechanical energy, there is an efficiency and temperature related.

Important thing is like this.

Is statistical mechanics total energy difference 5^oCwater 1g minus 4^oCwater 1g is 4.184J?

[CaptainPanic]

1 mile <===== 1.609344 kilometers

1 inch <===== 2.54 centimeters

1 bar <===== 750.2838 mmHg

1 cal <===== 4.18 J

 

That's just how it is.

 

Also, it's possible to change the units of temperature, for example Celsius to Fahrenheit... but you need a formula.

 

The next question is: why did they choose the Calorie as a unit for energy???

The reason is that it was practical. Someone (Mr. Celsius) had found a practical scale for temperature, using the freezing (0 C) and boiling point (100 C) for water.

Then they called 1 degree C increase for 1 gram of water 1 calorie. It seemed practical.

 

Later, in France the metric system was invented (click for a quick wikipedia history lesson)... and it was found that a number of units wouldn't be used anymore, like the grave for weight, the foot for distance and the calorie for energy. Instead, the kilogram, the meter and the Joule were used.

Edited January 28, 2011 by CaptainPanic