Thermodynamics Flashcards
What is thermite ?
- Metal powder and metal oxide
- Exothermic reduction-oxidation (redox) reaction
Thermite equation
- Fe2O3 + 2 Al → 2 Fe + Al2O3 + HEAT
What is thermodynamics ?
- is the science of the relationship
between heat and other forms of energy.
What is thermochemistry ?
- is the study of the quantity of heat
absorbed or evolved by chemical reactions
Radiant energy
- comes from the sun and is earth’s
primary energy source.
Thermal energy
- is the energy associated with the
random motion of atoms and molecules
Chemical energy
- is the energy stored within the bonds of chemical substances
Nuclear energy
- is the energy stored within the collection of neutrons and protons in the atom.
Potential energy
- is the energy available by virtue of an object’s position
What is energy ?
- The capacity to supply heat or do work.
Kinetic Energy (EK)
- The energy of motion
Potential Energy (EP)
- Stored energy
Thermal Energy
- The kinetic energy of molecular motion,
measured by finding the temperature of an object.
What is heat ?
- The amount of thermal energy transferred from one object to another as the result of a temperature difference between the two
Law of Conservation of Energy
- Energy cannot be created or destroyed; it can only be converted from one form to another.
First Law of Thermodynamics
- Energy cannot be created or destroyed; it can only be converted from one form to another
What is an isolated system ?
- can neither do work upon nor heat their
surroundings
The internal energy of an isolated system is
- constant
Change in energy equation
∆E = Efinal - Einitial
What is an exothermic process ?
- change (e.g. a chemical reaction) that releases heat
What does a release of heat correspond to ?
- decrease in enthalpy
What is an endothermic process ?
- a change (e.g. a chemical reaction) that requires (or absorbs) heat.
What does an input of heat correspond to ?
- an increase in enthalpy
What is enthalpy ?
- the measurement of energy in a thermodynamic
system.
What is an open system ?
- Can exchange both matter and energy with the
surroundings (e.g. open reaction flask, rocket engine)
What is a closed system ?
- Can exchange only energy with the surroundings (matter remains fixed) e.g. a sealed reaction flask.
What is an isolated system ?
- Can exchange neither energy nor matter with
its surroundings (e.g. a thermos flask).
What is state function ?
- A function or property whose value depends
only on the present state, or condition, of the system, not on the path used to arrive at that state.
Equation for work ?
- work = force x distance
What is expansion work ?
- Work done as the result of a volume change in the system.
- Also called pressure-volume or PV work.
Equation for ∆E
∆E = q + w
Equation for q ?
- q = ∆E + P∆V
What is q ?
- heat transferred
Equation for w ?
- -P∆V
What is ∆ H ?
- heat given off or absorbed during a reaction at constant pressure
What is the pressure in a vacuum ?
- 0 atm
Thermodynamic Standard State
- Most stable form of a substance at 1 atm pressure (po)
- at a specified temperature, usually 25°C
- 1M concentration for all substances in solution
What is Hm ?
- Standard Molar Enthalpy of a substance.
What are phase transitions accompanied by ?
- Most phase transitions are accompanied by a change in enthalpy
Enthalpy of Fusion (∆Hfusion)
- The amount of heat necessary to melt a substance without changing its temperature.
Enthalpy of Vaporization (∆Hvap)
- The amount of heat required to vaporize a substance without changing its temperature.
Enthalpy of Sublimation (∆Hsubl)
- The amount of heat required to convert a
substance from a solid to a gas without going through a liquid phase.
Is ∆ H negative or positive for endothermic reactions ?
- positive
What is the equation for ∆Hsubl ?
- ∆Hsubl = ∆Hfusion + ∆Hvap
Is ∆ H negative or positive for exothermic reactions ?
- negative
What happens if you reverse a reaction ?
- the sign of ∆H changes
