The First Law of Thermodynamics
|What does conservation of energy mean? It means that as a system exchanges energy with its environment through heat flow or thermodynamic work (pressure-volume work), there must be a corresponding loss or gain within the system. Think about it. This is just common sense. If heat is flowing into a system at constant volume (no work), the internal energy of the system must be increasing. If heat is flowing out, the internal energy of the system must be decreasing. If the surroundings perform work on the system and heat flow is prevented, the change in internal energy must equal the work that is being done on the system. Usually there is some combination of heat flow and work occuring in a thermodynamic transformation. Sum it up, keeping the plus and minus signs straight because by convention positive work and negative heat flow both cost the system energy. The internal energy change equals the sum. The first law of thermodynamics is just common sense.|
Whether an MCAT passage deals with a steam engine or a phase diagram, if an MCAT passage has a theme directly concerned with thermodynamics, there will be a question or two requiring you to reason from the 1st Law, guaranteed. And this is important for those qeustions, but it is trivial compared to the importance of understanding thermodynamics for understanding science, which will affect your performance through the entire exam. Really concentrate here. When we move through the chemistry and into biochemistry later in this course, there will be a big payoff in your conceptual understanding if you really push here.