Energy can take several forms, and it can be converted from one form to another. All living organisms require and use energy in varied forms; for example, motion involves mechanical energy, and maintenance of body temperature uses thermal energy. Photosynthesis requires light energy from the Sun. Some organisms, such as several species of fish, are striking examples of the use of chemical energy to produce electrical energy (Figure 1.24). The formation and breakdown of biomolecules involve changes in chemical energy.
Any process that will actually take place with no outside intervention is spontaneous in the specialized sense used in thermodynamics. Spontaneousdoes not mean “fast”; some spontaneous processes can take a long time to occur.
The laws of thermodynamics can be used to predict whether any change involving transformations of energy will take place. An example of such a change is a chemical reaction in which covalent bonds are broken and new ones are formed. Another example is the formation of noncovalent interac-tions, such as hydrogen bonds, or hydrophobic interactions, when proteins fold to produce their characteristic three-dimensional structures. The tendency of polar and nonpolar substances to exist in separate phases is a reflection of the energies of interaction between the individual molecules-in other words, a reflection of the thermodynamics of the interaction.
A spontaneous reaction is one that will take place without outside inter-vention. This point does not specify reaction rate. Some spontaneous processes can take a long time to occur.