Chapter 8- Thermodynamics Flashcards
Define the term ‘system’
The system is the part of the universe being studied
Define the term ‘surroundings’
The surroundings are the rest of the universe that interacts with the system.
Name the three types of systems
Open
Closed
Isolated
What is meant by the term ‘open system’?
An open system is a system that freely exchanges energy and matter with its surroundings.
What is meant by the term ‘closed system’?
A closed system is a system that exchanges only energy with its surroundings, not matter
What is meant by the term ‘isolated system’?
An isolated system does not exchange energy or matter with its surroundings.
Define the term ‘internal energy’.
The internal energy (U) is the energy in a system arising from the relative positions and interactions of its parts.
ΔU=
U(products) – U(reactants)
State the first law of thermodynamics
For internal energy, U, heat, q, and work, w,
ΔU = q + w
If no work is done then the change in internal energy is equal to the heat transferred
ΔU = qV
What is enthalpy?
A thermodynamic quantity equivalent to the total heat content of a system. It is equal to the internal energy of the system plus the product of pressure and volume
H = U + pV
How do you measure enthalpy change?
ΔH = ΔU + Δ(pV)
= ΔU + pΔV
∴ ΔH = qp
What is the value of ΔH for endothermic reactions?
ΔH > 0
What is the value of ΔH for exothermic reactions?
ΔH < 0
State Hess’s law
The enthalpy change for a reaction is independent of the way that the reaction occurs
What are state functions?
A quantity in thermodynamics, such as entropy or enthalpy, that has a unique value for each given state of a system.
