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Internal Energy
Kaylene_5146
#1 Posted : Thursday, July 16, 2020 8:15:18 PM
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Chapter 4, p.134 has a bolded red text saying:

"The MCAT may refer to internal every as 'heat energy', 'internal energy', or 'heat'. Heat energy and thermal energy are really virbational, rotational, and translational parts of internal energy. They are called thermal energy because they affect temperature. Heat is a transfer of energy, and using it as another name for internal energy can create confusion. Unfortunately, this is a common mistake."

I find this text extremely confusing. If internal energy is composed of 6 types of energy (vibrational. translation, roatationa, electronic, intermolecular potential, and rest mass energy), but heat/ thermal energy is only referring to 3 (vibrational, rotational, translation), how is it possible that the MCAt will use the words heat energy and internal energy interchangeably?

In other words, if heat/ heat energy/ thermal energy comes up on the MCAT is it referring to all 6 aspects of internal energy or just the 3 aspects of heat energy?
INSTR_Katerina_102
#2 Posted : Friday, July 17, 2020 4:01:56 PM
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Hi Kaylene,

This can be confusing, and I would not read too deeply into it - EK tends to go into a little too much detail when describing some things, and this is one of these cases.

"The MCAT may refer to internal energy as 'heat energy', 'internal energy', or 'heat'. Heat energy and thermal energy are really vibrational, rotational, and translational parts of internal energy. They are called thermal energy because they affect temperature. Heat is a transfer of energy, and using it as another name for internal energy can create confusion. Unfortunately, this is a common mistake."

I find this text extremely confusing. If internal energy is composed of 6 types of energy (vibrational. translation, roatationa, electronic, intermolecular potential, and rest mass energy), but heat/ thermal energy is only referring to 3 (vibrational, rotational, translation), how is it possible that the MCAt will use the words heat energy and internal energy interchangeably?

When non experts refer to internal energy (deltaE) colloquially, they can mistakenly refer to it as heat content/energy/what have you because when you form intermolecular bonds you release heat, and when you consume mass you can make energy, thus they consider these "heat content" of the molecule. Note that the EK says that this is a common mistake. However, because the MCAT is written by people with a good knowledge of their fields, this shouldn't be a relevant mistake for people to make.

In other words, if heat/ heat energy/ thermal energy comes up on the MCAT is it referring to all 6 aspects of internal energy or just the 3 aspects of heat energy?

I cannot guarantee this either way - I think the likelihood that they will simply ask you what internal energy means is low. I think it also depends on the passage. If they refer to it as internal energy I would assume all 6 forces. If they refer to heat energy, it is possible they mean all 6 but they will likely mean just the 3 of translation rotation vibration.

Please let me know if this is unclear.

Katt
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