Thermodynamics Flashcards
(21 cards)
Equation for internal energy of a system?
U = w + q
Internal energy = work + heat
What is kinetic energy?
E = mv^2
A particle with both mass and velocity
Name 2 types of potential energy.
- Gravitational potential
2. Chemical bond energy (energy stored in chemical bonds
What happens to the energy during bond formation and bond cleavage?
Bond formation releases energy
Bond cleavage requires energy
What is an open energy system?
A system where both matter and energy can be transferred between the system and the surroundings
What is a closed energy system?
A system where only energy can be transferred between the system and the surroundings
What is an isolated system?
A system where neither matter nor energy can be transferred between the system and the surroundings
What is the 1st law of thermodynamics and what does it state?
Conservation of energy - energy cannot be created or destroyed and can only be transformed between different forms.
What is work?
Any process that can be used to lift a weight
How does work affect energy transfer?
Energy is transferred from the system to its surroundings
What is the equation for work?
Work = force x distance
What is the equation for force?
Force = mass x acceleration Force = k x q1 x q2 / r^2
k = coulombs, q = magnitudes of the charges (+ or -), r = distance between charges
What happens when a hot system comes in contact with a colder surround and vice versa?
The hot system will spontaneously get colder however the reverse will not happen and so the cold system will not get colder
What is the equation for energy derived from pressure and volume changes?
Energy = pressure x volume
What is enthalpy?
In thermodynamics, it’s a measure of the heat content of a chemical or physical system
What is the equation for the enthalpy of a system?
H = U + pV
H = enthalpy/heat, U = internal energy, p = pressure, V = volume
What is the definition of the change of enthalpy?
△H = △U + p△V
H = enthalpy/heat, U = internal energy, p = pressure, V = volume
Only the change in volume is important as in chemistry most measurements are made at constant pressure.
What happens in an endothermic reaction?
Energy is absorbed from surroundings to break bonds
△H > 0
What happens in an exothermic reaction?
Energy is released into the surroundings from bond formation
△H < 0
What is Hess’s law?
Hess’s law states that the enthalpy change for a chemical reaction is independent of the route taken. This means that the enthalpy change for the overall process will be identical regardless of how many steps are taken
What is used to measure enthalpy changes?
A bomb calorimeter
