work

Examples of work in the following topics:

• Free Energy and Work

  • The Gibbs free energy is the maximum amount of non-expansion work that can be extracted from a closed system.
  • The work is done at the expense of the system's internal energy.
  • Energy that is not extracted as work is exchanged with the surroundings as heat.
  • "Useful" in this case, refers to the work not associated with the expansion of the system.
  • This is most commonly electrical work (moving electric charge through a potential difference), but other forms of work are also possible.

• Heat and Work

  • Like heat, the unit measurement for work is joules (J).
  • There are many forms of work, including but not limited to mechanical, electrical, and gravitational work.
  • For our purposes, we are concerned with P-V work, which is the work done in an enclosed chemical system.
  • Heat and work are related.
  • Work can be completely converted into heat, but the reverse is not true: heat energy cannot be wholly transformed into work energy.

• Pressure and Free Energy

  • Gibbs free energy measures the useful work obtainable from a thermodynamic system at a constant temperature and pressure.
  • Just as in mechanics, where potential energy is defined as capacity to do work, similarly different potentials have different meanings.
  • The Gibbs free energy is the maximum amount of non-expansion work that can be extracted from a closed system.
  • When a system changes from an initial state to a final state, the Gibbs free energy (ΔG) equals the work exchanged by the system with its surroundings, minus the work of the pressure force.

• Comparison of Enthalpy to Internal Energy

  • Internal energy is generally represented as the sum of work and heat done by or to the system.
  • where w represents work and q represents heat.
  • Similarly, +w means work is done on the system, while -w means work is done by the system.
  • For example, if a reaction is held at constant volume, no work is performed and therefore $\Delta U=q$.
  • So, even if the heat change can be measured, $\Delta U\neq q$ because some work has been performed.

• Lab safety

  • To introduce safety concerns to students who will be working with harmful chemicals.

• Internal Energy and Enthalpy

  • In thermodynamics, work (W) is defined as the process of an energy transfer from one system to another.
  • In this equation, U is the total energy of the system, Q is heat, and W is work.
  • In chemical systems, the most common type of work is pressure-volume (PV) work, in which the volume of a gas changes.
  • Substituting this in for work in the above equation, we can define the change in internal energy for a chemical system:
  • By adding the PV term, it becomes possible to measure a change in energy within a chemical system, even when that system does work on its surroundings.

• Changes in the Entropy of Surroundings

  • Although the system can always be restored to its original state by recompressing the gas, this would require that the surroundings perform work on the gas.
  • Since the gas does no work on the surroundings in a free expansion (the external pressure is zero, so PΔV = 0,), there will be a permanent change in the surroundings.
  • Another example of an irreversible change is the conversion of mechanical work into frictional heat; there is no way, by reversing the motion of a weight along a surface, that the heat released due to friction can be restored to the system.

• The Three Laws of Thermodynamics

  • A way of expressing the first law of thermodynamics is that any change in the internal energy (∆E) of a system is given by the sum of the heat (q) that flows across its boundaries and the work (w) done on the system by the surroundings:
  • This law says that there are two kinds of processes, heat and work, that can lead to a change in the internal energy of a system.
  • Since both heat and work can be measured and quantified, this is the same as saying that any change in the energy of a system must result in a corresponding change in the energy of the surroundings outside the system.
  • If heat flows into a system or the surroundings do work on it, the internal energy increases and the sign of q and w are positive.
  • Conversely, heat flow out of the system or work done by the system (on the surroundings) will be at the expense of the internal energy, and q and w will therefore be negative.

• Carbon-Carbon Bond Formation

  • The 2010 Nobel Prize in chemistry was jointly awarded to Heck, Negishi and Suzuki for their work in developing these coupling reaction
  • The Reppe work is outlined in equation # 1 of the first diagram.
  • The best nickel catalyst was Ni(CO)4, a toxic gas, and recent work by K.P.C.

• Discovery of Radioactivity

  • While working on phosphorescent materials, he happened to place the pitchblende on black paper that he had used to cover a piece of film.
  • Over four years, working under poor conditions and spending their own funds, the Curies processed more than a ton of uranium ore to isolate a mere gram of radium salt.
  • Shortly after Marie completed her PhD, both Curies and Becquerel shared the 1903 Nobel Prize in Physics for their work on radioactivity.