Thermodyanmics, thermal properties of matter

In summary, the minimum amount of energy that must be removed to produce solid ethyl alcohol is 52866.8J. However, this calculation is based on a mistaken value for the melting/freezing point of -114 degrees, which should actually be -134 degrees. Correcting this error would result in the expected answer of 68000J.
  • #1
Jennifer001
22
0

Homework Statement


a beaker contains 200mL of ethyl alcohol at 20degrees. what is the minumum amount of energy that must be removed to produce solid ethyl alcohol..

the melting/freezing pt is 114degrees Lf=1.09x10^5
density is 790kg/m^3
specific heat cap = 2400J/kgK

Homework Equations


Q=mcdT
Q=ML
m=pv

The Attempt at a Solution


m=pv=(2.00*10^-4m^3)(790)=0.158kg
Q1=mcdT
=0.158(2400)(94)
=35644.8J
Q2=ML
=0.158(1.09*10^5)
=17222J

Qtotal=Q1+Q2
=52866.8J

i think i did somethign wrong because in the book it says the answer is 68000J can someone help me out i don't know what i did wrong?
 
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  • #2
Jennifer001 said:

Homework Statement


a beaker contains 200mL of ethyl alcohol at 20degrees. what is the minumum amount of energy that must be removed to produce solid ethyl alcohol..

the melting/freezing pt is 114degrees

That 114 degrees must be wrong. If it were true, it would already be a solid at 20 degrees.

Lf=1.09x10^5
density is 790kg/m^3
specific heat cap = 2400J/kgK

Homework Equations


Q=mcdT
Q=ML
m=pv

The Attempt at a Solution


m=pv=(2.00*10^-4m^3)(790)=0.158kg
Q1=mcdT
=0.158(2400)(94)
=35644.8J
Q2=ML
=0.158(1.09*10^5)
=17222J

Qtotal=Q1+Q2
=52866.8J

i think i did somethign wrong because in the book it says the answer is 68000J can someone help me out i don't know what i did wrong?
 
  • #3
Redbelly98 said:
That 114 degrees must be wrong. If it were true, it would already be a solid at 20 degrees.


oooh sorry that 114 is suppose to be -114
 
  • #4
Jennifer001 said:
oooh sorry that 114 is suppose to be -114

Okay, then do you see the error here:

Jennifer001 said:
Q1=mcdT
=0.158(2400)(94)
=35644.8J
 
  • #5
Redbelly98 said:
Okay, then do you see the error here:

oo i added it wrong for dT its suppose to be -114-20 instead of 114-20

ok thank you
 

1. What is thermodynamics?

Thermodynamics is the branch of physics that deals with the study of heat and its relation to other forms of energy. It also includes the study of how heat is transferred and how it affects the properties of matter.

2. How are thermal properties of matter measured?

Thermal properties of matter, such as specific heat capacity and thermal conductivity, are measured through various experimental methods. These include calorimetry, thermal conductivity measurements, and differential scanning calorimetry.

3. What is the difference between heat and temperature?

Heat is a form of energy that is transferred from one object to another due to a difference in temperature. Temperature, on the other hand, is a measure of the average kinetic energy of the particles in a substance.

4. How does thermodynamics relate to everyday life?

Thermodynamics has many practical applications in everyday life, such as in heating and cooling systems, cooking, and energy production. It also helps us understand the behavior of gases, liquids, and solids under different conditions.

5. What is the second law of thermodynamics?

The second law of thermodynamics states that in any natural process, the total entropy (disorder) of a closed system will always increase over time. This is often referred to as the law of increasing entropy.

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