Answer to Question #229100 in General Chemistry for Mickayla Ennis

Question #229100

A system delivers 225 J of heat to the surroundings while delivering 645 J of work. Calculate the change in the internal energy, Δ E, of the system

  1. -420 J
  2. 420 J
  3. -870 J
  4. 870 J
1
Expert's answer
2021-08-24T06:16:41-0400

The energy balance from the First Law of Thermodynamics states that the total internal energy "\u0394U" of a system is equal to the energy input minus energy output.

This is the heat "Q" minus the work performed "W". Mathematically,


"\u0394U=Q\u2212W"


In this system, heat is lost to the surrounding, which means that "Q" is negative. Work being delivered to the surroundings means "W" is positive.


Therefore, if "Q\n\n=\n\n\u2212\n\n225\n\n \n\nJ" and "W=+645 J" , then the change in internal energy is:


"\u0394U=\u2212225 J\u2212(+645 J)= \u2212870 J"

 

The change in internal energy of the system is (3). -870 J.

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