akimhaneul

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should we learn this for mcat? or is PV diagram enough?
 

aldol16

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I think being able to read a P-V diagram should be enough. You should be able to reason through it.
 

NextStepTutor_2

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should we learn this for mcat? or is PV diagram enough?
Hi @akimhaneul !

The AAMC can and has asked about Carnot cycles, heat engines, and thermodynamics in this context. More important, however, is to understand the differences between adiabatic/isothermal/isobaric processes and expansion/compression and their associated thermodynamic changes. Understanding these will allow you to spot them in any context.

For example, the PV diagram for hart contraction is a much more medically relevant application of these principles than a simple heat engine, and thus, more likely to show up on the new MCAT. Use the Carnot cycle to understand these concepts, do not just memorize it.



Hope this helps, good luck!
 
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akimhaneul

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Hi @akimhaneul !

The AAMC can and has asked about Carnot cycles, heat engines, and thermodynamics in this context. More important, however, is to understand the differences between adiabatic/isothermal/isobaric processes and expansion/compression and their associated thermodynamic changes. Understanding these will allow you to spot them in any context.

For example, the PV diagram for hart contraction is a much more medically relevant application of these principles than a simple heat engine, and thus, more likely to show up on the new MCAT. Use the Carnot cycle to understand these concepts, do not just memorize it.



Hope this helps, good luck!
Thanks I think I'm having trouble understanding the overall significance of the carnot cycle relating it to real life examples such as refrigerators. :(
 

aldol16

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Thanks I think I'm having trouble understanding the overall significance of the carnot cycle relating it to real life examples such as refrigerators. :(
Okay, so whenever a gas undergoes isothermal expansion or compression, it takes on or releases heat from the environment. Think about it. To expand, a gas needs to take on heat from its surroundings. Similarly, when a gas is compressed, it releases heat into the surroundings. So imagine a square section of pipe. On one side, you expand the gas and on the other side, you compress it. This square pipe is bisected so that you have two compartments. So on the side the gas is expanding, it takes on heat from that compartment. Then on the other side, you compress the gas. This releases the heat into that compartment. Keep doing this in a cycle and one compartment will get cold while the other one gets hot.
 
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akimhaneul

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Okay, so whenever a gas undergoes isothermal expansion or compression, it takes on or releases heat from the environment. Think about it. To expand, a gas needs to take on heat from its surroundings. Similarly, when a gas is compressed, it releases heat into the surroundings. So imagine a square section of pipe. On one side, you expand the gas and on the other side, you compress it. This square pipe is bisected so that you have two compartments. So on the side the gas is expanding, it takes on heat from that compartment. Then on the other side, you compress the gas. This releases the heat into that compartment. Keep doing this in a cycle and one compartment will get cold while the other one gets hot.
Ok thanks then what's happening in the adiabatic section of the carnot cycle compared to the isothermal section? I think I never understood the relationship between these sections
 

aldol16

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Ok thanks then what's happening in the adiabatic section of the carnot cycle compared to the isothermal section? I think I never understood the relationship between these sections
For the purposes of a refrigerator, the adiabatic section just serves to connect the two isothermal ones. The isothermal sections are the crucial components of actual refrigeration.
 
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akimhaneul

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For the purposes of a refrigerator, the adiabatic section just serves to connect the two isothermal ones. The isothermal sections are the crucial components of actual refrigeration.
Ok thanks it makes so much more sense.

Also, it says that heat pump follows a counterclockwise path whereas heat engine follows a clockwise path on pv diagram. How can you tell from those diagrams that heat engine takes heat and converts it into work and heat pump takes work and converts it into heat?


Also, is adiabatic section just something there for connecting the isothermal sections and not really that important in a Carnot cycle?

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TheLongGame

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Ok thanks it makes so much more sense.

Also, it says that heat pump follows a counterclockwise path whereas heat engine follows a clockwise path on pv diagram. How can you tell from those diagrams that heat engine takes heat and converts it into work and heat pump takes work and converts it into heat?


Also, is adiabatic section just something there for connecting the isothermal sections and not really that important in a Carnot cycle?

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The adiabatic "legs" are definitely important! But probably not so much for the MCAT. The Carnot cycle has to be reversible, and so the isothermal expansion must be followed by an adiabatic (and isentropic) expansion that allows the medium to cool with no loss of heat to the environment. Likewise, to complete the cycle, the isothermal compression must be followed by adiabatic compression to return to your initial state.


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