The internal energy of any system is the capacity of the system to do work or release heat.
The internal energy is the sum of the kinetic and potential energy of the system.
It is convenient when discussing internal energy changes to divide the universe into the system and the surroundings.
The change in the internal energy (U) of the system can be represented mathematically by: ΔU = q + w
The internal energy is the sum of the kinetic and potential energy of the system.
The kinetic energy of chemical systems is due to the motion of the molecules and the atoms within those molecules.
Even ions in the lattice of ionic solids are in constant motion.
The potential energy of chemical systems is largely due to the attraction between positive and negative particles.
Bringing these particles closer together decreases the potential energy of the system.
Thus the atoms in a bond have lower potential energy than the separated atoms.
Gas molecules have higher potential energy than liquid molecules because they are separated to a greater extent.
Internal energy cannot be measured directly, but it is possible to measure changes in internal energy.Even ions in the lattice of ionic solids are in constant motion.
The potential energy of chemical systems is largely due to the attraction between positive and negative particles.
Bringing these particles closer together decreases the potential energy of the system.
Thus the atoms in a bond have lower potential energy than the separated atoms.
Gas molecules have higher potential energy than liquid molecules because they are separated to a greater extent.
One statement of the first law of thermodynamics says that the total energy of the universe is constant.
Therefore when the energy of some part of the universe is increased, another part must have a corresponding decrease in energy.
Therefore when the energy of some part of the universe is increased, another part must have a corresponding decrease in energy.
In chemistry, the chemical reaction is the system, and the container and/or the solution in which the reaction is carried out is the surroundings.
The system and the surroundings for a coffee-cup calorimeter are shown at the right.
Energy can be transferred between the system and the surroundings in two ways.The system and the surroundings for a coffee-cup calorimeter are shown at the right.
Through transfer of heat (q)
Through work (w) being done on or by the system
Through work (w) being done on or by the system
The change in the internal energy (U) of the system can be represented mathematically by: ΔU = q + w
q is positive if heat is transferred TO the system from the surroundings (as in an endothermic reaction)
q is negative if heat is transferred FROM the system to the surroundings (as in exothermic reactions)
w is positive if work is done ON the system (as when a gas is compressed by a piston)
Work is done on the system in a chemical reaction system if there are fewer gas molecules in products than in reactants.
w is negative if work is done BY the system (as when a gas expands against a constant pressure)
Work is done by the system in a chemical reaction system if there are more gas molecules in the products than in the reactants.
q is negative if heat is transferred FROM the system to the surroundings (as in exothermic reactions)
w is positive if work is done ON the system (as when a gas is compressed by a piston)
Work is done on the system in a chemical reaction system if there are fewer gas molecules in products than in reactants.
w is negative if work is done BY the system (as when a gas expands against a constant pressure)
Work is done by the system in a chemical reaction system if there are more gas molecules in the products than in the reactants.