Laws of Thermodynamics and General Concepts
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Physics › Laws of Thermodynamics and General Concepts
What is the change in entropy for  of ice initially at 
 that melts to water and warms to the temperature of the atmosphere at 
?
Latent heat of fusion for water: 
Specific heat of water: 
Specific heat of ice: 
Explanation
- We must account for two separate processes since the ice is melting and then warming. The basic formula to calculate the change in entropy at a constant temperature when the ice melts is:
 
Where  is the change in entropy, 
 is the change in heat energy, and 
 is the temperature at which the change of state for the ice occurs. Now we substitute in an equation for 
 for when ice melts: 
. Our entropy equation now becomes:
Now we plug in our known values into the equation:
Mass 
Latent heat of fusion 
Temperature 
And we get the change in entropy for the ice melting at a constant temperature, which is 
- Now we need to calculate the change in entropy for the liquid water warming from 
to
.
 
The basic formula to calculate the change in entropy at a changing temperature when the water warms is:
Next we substitute in an equation for  when there is a temperature change, but not a change in state. That equation is: 
 so our entropy equation now becomes:
next we integrate this equation to get:
Next we plug in the values we know and solve for the change in entropy:
Final temperature of water 
Initial temperature of water 
Specific heat of water 
Mass of water 
Now we get the change in entropy for the water warming to be 
We add our two entropy values together to find the total change in entropy to be:
A  steel sword is cooled from 
 to 
 by dipping it in 
 of water that is at 
.
If the specific heat of the steel is  and the specific heat of water is 
, what will be the temperature of the water after the steel is cooled?
Explanation
This is a simple pairing of two  equations.
We will make the left side for the steel and the right side for water. Thus:
Solving for  of water yields 
, and certainly the water gained heat not lost it, so the final temperature of the water is 
A steel beam is  long at a temperature of 
. On a hot day, the temperature reaches 
. What is the change in the beam's length due to thermal expansion given that the thermal expansion coefficient for steel is 
Explanation
We need to use the equation for thermal expansion in order to solve this problem:
We are given:
 for the thermal expansion constant
 for the initial length of the steel.
We need to calculate  which is the the difference of the two temperatures.
Now we have enough information to solve for the change in the length of steel.