Grade 11 Thermodynamics Question

In summary, Grade 11 Thermodynamics is the study of energy and its transformation in various systems. This branch of physics focuses on concepts such as heat, work, and temperature, and how they relate to each other in different processes. It also explores the laws of thermodynamics, which govern the behavior of energy in closed systems. Some key topics covered in this subject include heat transfer, thermodynamic cycles, and the properties of gases. Understanding thermodynamics is crucial in fields such as engineering, chemistry, and environmental science.
  • #1
The Spanglock
3
0

Homework Statement


You add 50 g of steam at 150 degrees centigrade to 50 g of ice at negative five degrees centigrade. What is the final temperature?

Homework Equations


Q = mLfv
Q = mcΔT

The Attempt at a Solution


Qg = Ql
Q1 + Q2 = -Q3 - Q4
mLf + mcΔT = -mLv + mcΔT [ΔT will be negative, making the symbol positive in front]
(0.05)(3.4x105) + (0.05)(4200)(Tf+ 5) = (0.05)(2.26x106) + (0.05)(4200)(Tf - 150)
210Tf + 18 050 = 210Tf -154 600

And I think that here you can see the issue. I asked my instructor since I previously had ...= -mLf - mcΔT, but that gave -232 degrees centigrade.

I'm hoping someone on here can help me. I always get stuck with these problems and the test is in two days, meaning I need to really understand these types of exercises or I'm screwed [these are ranked as the highest marked].

Thanks for any help you can offer! :smile:
 
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  • #2
You can try doing it by stages ... The energy from the steam is used to heat the ice.
How much energy would be released lowering the steam temperature to 100deg?
How much energy is needed to raise the ice temperature to 0deg?
Is the first number bigger or smaller than the second one?

You can also try sketching a graph of energy vs temperature ... you will have two lines, one for energy released by the steam and the other for energy needed by the water. The two lines will have sloping and horizontal sections ... and they should cross somewhere.
 
  • #3
Simon Bridge said:
You can try doing it by stages ... The energy from the steam is used to heat the ice.
How much energy would be released lowering the steam temperature to 100deg?
How much energy is needed to raise the ice temperature to 0deg?
Is the first number bigger or smaller than the second one?

You can also try sketching a graph of energy vs temperature ... you will have two lines, one for energy released by the steam and the other for energy needed by the water. The two lines will have sloping and horizontal sections ... and they should cross somewhere.
I sketched a graph, which my instructor looked at. He said it's good and that I'm on the right track, but I don't know what it is I'm doing wrong. I tried fiddling with the positive and negative signs to see if I could at least get a reasonable answer with no luck. I just tried to do it in some stages and it didn't work as well. I have never been stuck on a problem so long before in my life.
 
  • #4
OK - show me the stages ... please answer the questions in post #2.
 
  • #5
Simon Bridge said:
OK - show me the stages ... please answer the questions in post #2.
I did each one individually, as my teacher taught me to do. I'm not sure if this is what you meant, but I'll show you anyway.

Q1 = mLf = (0.05)(3.4x106) = 17 000
Q2 = mcΔT = (0.05)(4200)(Tf+5) = 210Tf + 1050
Q3 = -mLv = -(0.05)(2.26x106) = -113 000
Q4 = mcΔT = (0.05)(4200)(Tf -160)

Then I subbed them in. Is this what you meant? Do all the calculations separately then combine them? Or did I misinterpret?
 
  • #6
No, when I say please answer the questions in post #2 I mean answer the questions in post #2.
None of those lines answer the questions in post #2?

Lets do it one at a time:
1. How much energy is released lowering the steam to 100deg?

The idea here is to make sure you understand the process.

Aside: check your values for specific and latent heats ... check units etc.
i.e. I have L_f = 334 kJ/kg = 3.34x105 J/kg
from http://www.engineeringtoolbox.com/water-thermal-properties-d_162.html
Compare with yours.

The numbers in post #5 seem to assume the initial temp of the steam is 160deg (that is not what post #1 says) and that the specific heats are the same across phase changes, and that all the steam and all the ice ends up as water.
 
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What is thermodynamics?

Thermodynamics is the study of the relationships between heat, work, energy, and their transformations.

What topics are covered in Grade 11 thermodynamics?

Grade 11 thermodynamics typically covers the laws of thermodynamics, heat and temperature, thermal energy, and heat transfer.

What are the laws of thermodynamics?

The first law states that energy cannot be created or destroyed, only transferred or transformed. The second law states that the total entropy of an isolated system can never decrease over time. The third law states that as the temperature approaches absolute zero, the entropy of a pure crystalline substance approaches zero as well.

What is the difference between heat and temperature?

Heat is the transfer of thermal energy from a hotter object to a cooler object, while temperature is a measure of the average kinetic energy of particles in a substance.

What are the different types of heat transfer?

The three main types of heat transfer are conduction, convection, and radiation. Conduction is the transfer of heat through direct contact, convection is the transfer of heat through the movement of fluids, and radiation is the transfer of heat through electromagnetic waves.

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