The study of energy changes in various systems (phase changes, chemical reactions, and nuclear changes)
Thermochemistry
The study of energy changes for chemical reactions
Thermodynamics is very important since every day energy is used in the form of heat (fossil fuels), light (fireflies), mechanical (internal combustion engines) and electrical (batteries) energy
If the temperatures of the 2 items are close
The rate of heatexchange will be slower
Energy
The capacity to dowork or supplyheat
Temperature (T)
A measure of the average kinetic energy of the particles in a system. Temperature is independent of the amount of material present.
Kinetic Energy (EK)
Energy of motion. It results from the movement of particles. The average kinetic energy differs between gases, liquids, and solids of the same substance. EK, (gas) > EK (liquid) > EK (solid)
Work (w)
Energy exchanged by mechanical means. Involves the application of a force that is associated with the movement of an object by a specific distance
Temperature only depends on speed
Heat (Q)
Thermal energy that is transferred between objects when a difference in temperature exists. Heat depends on the amount of material that is present.
Heat is transferred from a hotter object to a colder object
The temperature of the hotter object will decrease while the temperature of the colder object will increase until both objects reach the same temperature (equilibrium temperature)
The hotter object originally possesses a greater average Ek than the colder object
Ek is transferred from the object with greater average Ek to the object with lower average Ek until both have the same average Ek (equilibrium is established)
A bucket of 50 C water would be better at heating a swimming pool than a cup of 100 C water
System
The part of the universe that we choose to study
Chemical System
The substance, or group of substances, undergoing change
Surroundings
The parts of the universe with which the system interacts (everything in the universe that is not part of our system)
A system does NOT contain heat or work
Heat and work are the means by which a system exchanges energy
Heat and work exist only as changes (ΔT for heat, Δ position for work)
Internal energy, E
The total energy contained within a system (substance) = kinetic energy (EK) + potential energy (EP)
Kinetic energy (EK)
Energy of motion of the particles
Potential energy (EP)
Energy in the form of attractions between atoms/ions (chemical bonds) and between molecules (intermolecular forces)
The First Law of Thermodynamics
ΔE = Q + w
Energy entering a system
Is associated with a positive sign. If the system absorbs heat then Q>0 (endothermic)
Energy leaving a system
Is associated with a negative sign. If the system releases heat, then Q<0 (exothermic)
The First Law of Thermodynamics arises from The Law of Conservation of Energy
ΔEuniverse = 0
Euniverse = Esystem + Esurroundings
Energy cannot be created or destroyed, only transformed
In interactions between a system and its surroundings the total energy remains constant
Energy is neither created nor destroyed, but can be converted from one form to another or transferred between a system and its surroundings
Qsystem + Qsurroundings = 0
Qsystem = - Qsurroundings (heat lost = heat gained)
example of an exothermic reaction:
Hand warmers, the system (handwarmers) transfer heat to the surroundings (hands), leading to an increase in temperature of the surroundings but a decrease in temperature of the system
Thermal energy is the total kinetic energy of the particles in an object, directly related to the amount of matter in the object