Thermodyanmics, thermal properties of matter

[Jennifer001]

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?

 

[Redbelly98]

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?

 

[Jennifer001]

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

 

[Redbelly98]

oooh sorry that 114 is suppose to be -114

Okay, then do you see the error here:

Q1=mcdT
=0.158(2400)(94)
=35644.8J

 

[Jennifer001]

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