Why is vaporization endothermic? Why is condensation exothermic?
2 Answers
Vaporization requires energy to break the bonds holding a molecule together in a liquid, Condensation releases energy as liquid molecules have much less kinetic energy than gaseous molecules.
Explanation:
Endothermic means heat in. Vaporization like melting requires energy to be put in for the molecules to change state from liquid to gas. The temporary bonds between liquid molecules must be broken for the liquid to change to a gas this requires energy to be put into the system, ( endothermic)
Exothermic means heat out. Condensation like freezing releases heat. The gaseous molecules must release large amounts of kinetic energy to slow down enough to form the temporary bonds required to become a liquid. The extra heat goes out of the system into the surrounding environment. ( Exothermic.)
Because gaseous particles possess more kinetic energy than those in a liquid state.
Explanation:
In a solid particles have the lowest amount of energy relative to those in a liquid state and a gaseous state (the highest amount of energy of the three states). Bonds require energy to break and release energy when being formed. To form a liquid from a solid, we need to break bonds and to form a gas from a liquid we need to break even more bonds. This requires a higher input of energy each time more bonds are broken.
Endothermic processes ( graph A ) are where energy is absorbed by a system / reactants and the energy of the particles involved is higher than before the process occurred.
Exothermic processes ( graph B ) are the opposite of endothermic processes - energy is released by a system / reactants and the particles involved have a lower energy after the process than before.
Linking this to solid, liquid and gas states, when you vaporise a substance (turn it into a gas) you are promoting the particles in the substance to a state whereby they will possess more energy. This energy has to 'come' from somewhere and so energy is taken in from the surroundings of the process. With state changes, this is usually in the form of heat (although pressure can be also be factored in).
Condensation is a gas turning into a liquid and so thus a high energy 'state' of particles becoming a lower energy 'state' of particles. If the overall energy of the particles involved is lower than before the process occurred, energy must have been released and thus the process can be considered exothermic.
