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### Course: AP®︎/College Physics 2>Unit 1

Lesson 3: Thermodynamic processes

# First law of thermodynamics problem solving

First law of thermodynamics problem solving. Created by David SantoPietro.

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• in the last question we are to find the heat added but the answer is in negative so that means we have calculated the heat loss, which isn't exactly the answer. We needed to find heat added not lost?
• You had to find the heat....Since the work is positive (work done on the system) and you know that the change in internal energy is negative (the average kinetic energy of the gas molecules is lower than it previously was) then you are expected to get a negative q (heat lost)...
• At , you say there is positive work done on the gas. If a gas is being compressed isn't the work required to do that negative? If you define the system as the gas itself? Because wouldn't the opposite be true that if the gas expands it does positive work?

I am confused based on a chart I am looking at in a Kaplan book that says work done by the system (expansion) = positive work and work done on the system (compression) = negative work
• Work done by the system (compression) is positive work after all by doing so the internal energy of the gas increases (a positive DU)....work done by the gas (expansion) is negative....
(1 vote)
• Determine ∆H2°298 of burning H2S process using meaning of the standard enthalpy change
H2S+3/2O2=So2+H2O
• a steam turbine recieves 32 kg of steam per minute with an enthalpy of 3714KJ/kg and a velocity of 30m/s. it leaves the turbine at 27 m/s and 3064 KJ/kg enthalpy. the radiation loss es 88620 kJ/hr. find the KW output.