Understanding Internal Energy Changes in Phases of Water

In summary: I think it would be safe to say that the mass would change depending on what phase it is in. But I'm not sure what the phrasing means by "relatives" and "in my notes". Do you know what they are?In summary, the Homework Equations show how energy changes for a fixed quantity of water in its three phases. The equation for internal energy alone is mc delta theta, and it doesn't change for a gas. The phrasing in the question may be referring to the mass being given in part B of the question, which is specific to water.
  • #1
SpiraRoam
57
0

Homework Statement


Sketch a diagram of internal energy (y-axis) versus temperature in the range from -10°C to +112°C to indicate how energy would change for a fixed quantity of water in its three phrases. Label and explain the main features of the variation.

Homework Equations


upload_2017-4-28_21-58-35.png


The Attempt at a Solution


I'm going to show how energy would hange over the 3 phases of freezing whilst a solid, melting from a solid and vapourising from a liquid as well as the triple point.

Thing is I'm not sure whether the first equation mc delta theta is the right one for internal energy alone? Would theta represent the change in absolute temperature from -273 degrees or the particles? I assume it's mass x speed of light x the change in absolute temp or something to do with the particles?

Or is another equation entirely?

Cheers
 
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  • #2
C in the equation is not the speed of light. Guess again.
 
  • #3
specific or just normal heat capacity?
 
  • #4
Day3091 said:
specific or just normal heat capacity?
Specific
 
  • #5
Okay, cheers. So that is definitely the equation used to find the internal energy of a quantity of water in whatever state? It doesn't change for a gas? There's
upload_2017-4-28_23-27-52.png
and it's relatives in my notes as well and I've got a feeling they may be relevant to gases.

Is theta the change in absolute temperature then?
 
  • #6
Day3091 said:
Okay, cheers. So that is definitely the equation used to find the internal energy of a quantity of water in whatever state? It doesn't change for a gas? There's View attachment 197422 and it's relatives in my notes as well and I've got a feeling they may be relevant to gases.

Is theta the change in absolute temperature then?
No. ##\Delta \theta## is the change in temperature.

You really need to do some studying in thermo book before you start working on this question. You are lacking the required background.
 
  • #7
Yeah you're right, I only gave it a general overview. Absolute temp is the difference from -273 degrees isn't it. So mass x specific heat capacity x change in temperature. I just need to find out how the mass changes in phases and states so I can calculate and begin to plot.

The thing is - a mass is only given in part B of the question (Specific capacity of water 4.19 kJ kg–1 K–1) and it isn't specified whether that applies to part A aswell...but it must do for the equation to work. How else am I going to get any values in Joules?
 
  • #8
Day3091 said:
Yeah you're right, I only gave it a general overview. Absolute temp is the difference from -273 degrees isn't it. So mass x specific heat capacity x change in temperature. I just need to find out how the mass changes in phases and states so I can calculate and begin to plot.

The thing is - a mass is only given in part B of the question (Specific capacity of water 4.19 kJ kg–1 K–1) and it isn't specified whether that applies to part A aswell...but it must do for the equation to work. How else am I going to get any values in Joules?
They only asked for a (rough) sketch.
 
  • #9
I hope so! It's hard to know whether to take the phrasing literally or not with it being science XD
 

FAQ: Understanding Internal Energy Changes in Phases of Water

1. What is the equation for internal energy?

The equation for internal energy is U = Q + W, where U represents the internal energy, Q represents heat, and W represents work.

2. How is the equation for internal energy derived?

The equation for internal energy is derived from the first law of thermodynamics, which states that the change in internal energy of a system is equal to the heat added to the system minus the work done by the system.

3. What are the units for internal energy?

The units for internal energy are joules (J) in the SI system. However, other unit systems, such as the calorie (cal) or British thermal unit (BTU), can also be used.

4. Can the equation for internal energy be used for all types of systems?

Yes, the equation for internal energy can be used for all types of systems, including closed, open, and isolated systems. It is a fundamental concept in thermodynamics and applies to all systems where energy can be transferred in the form of heat and work.

5. How is the equation for internal energy related to other thermodynamic quantities?

The equation for internal energy is closely related to other thermodynamic quantities, such as enthalpy and entropy. It is also related to temperature, as the internal energy of a system is proportional to its temperature. Additionally, the change in internal energy can be used to calculate the change in enthalpy and entropy through other thermodynamic equations.

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