Chemical Thermodynamics Flashcards
What is the first law of thermodynamics?
The amount of energy in the universe is constant. Energy can only be converted from one form to another; it cannot be created or destroyed
What is the unit of energy?
The joule (J)
What is 1J also equivalent to?
1 kg m^2 s^-2
What is a calorie?
A unit of energy equivalent to the heat energy required to raise the temperature of 1g of water by 1 degree C
What is universe generally equal to in thermodynamics?
System + Surroundings = Universe
What is system in thermodynamics?
System = the molecules that are to take part in the reaction, and the products formed from them
What is surroundings in the thermodynamics?
The rest of the universe
What is change in enthalpy equal to?
Change in enthalpy = Enthalpy of products - Enthalpy of reactants
If change in enthalpy is positive, the reaction is…
Endothermic
If change in enthalpy is negative, the reaction is…
Exothermic
What is the definition of enthalpy of combustion?
Enthalpy change when 1 mole of a compound is burned completely in oxygen
What is the definition of standard enthalpy of formation?
Enthalpy change when 1 mole of a substance is formed from its constituent elements
What does Hess’s Law state?
That enthalpy change involved in going from reactants to products in a given state is the same regardless of the path taken
What is entropy a measure of?
Entropy is a measure of disorder
How does entropy change through the states?
Most ordered = Solid < Liquid < Solution < Gas = Least ordered
What is C.I entropy of universe equal to?
C.I entropy of universe = C.I entropy of system + C.I entropy of surroundings
How is Gibbs free energy related to entropy and enthalpy?
Gibbs = C.I enthalpy - (T x C.I entropy)
At what values of Gibbs energy are reactions thermodynamically feasible?
A reaction will proceed if the system can lose free energy, I.e if C.I Gibbs free energy is negative
What does endergonic mean in terms of Gibbs?
Positive Gibbs energy = unfavourable
What does exergonic mean in terms of Gibbs?
Negative Gibbs energy = favourable
How can you work out the temperature at which a reaction is thermodynamically feasible using Gibbs energy?
If Gibbs energy < 0, the reaction is thermodynamically feasible. Therefore you can rearrange the Gibbs energy equation to make temperature the subject.
Temperature = C.I Enthalpy / C.I Entropy
What is reaction quotient?
The reaction quotient (Q) measures the relative amounts of products and reactants present during a reaction at a particular point in time
What is the formula for reaction quotient (Q)?
Reaction quotient = [Products]^(no. moles of each) / [Reactants]^(no. moles of each)
How are gases represented in the reaction quotient?
p[X]
How are solutions represented in the reaction quotient?
[X]
How are solids represented in the reaction quotient?
For solids, their concentration is 1, so they are not included in the reaction
What is the reaction relating Gibbs and equilibrium constant, and what does each symbol represent and what are the units?
Gibbs = -RTln(K)
R = gas constant = 8.314 (J mol^-1 K^-1)
T = temp (K)
K = equilibrium constant (J mol^-1)
How is the Gibbs-equilibrium constant rearranged to make equilibrium constant the subject?
K = e^(Gibbs/RT)
What is k equal to?
[Products]^(no. moles) / [Reactants]^(no. moles)
(at equilibrium)
What does a large equilibrium constant indicate?
The reaction will favour the forward direction
What does a small equilibrium constant indicate?
The reaction will favour the backwards direction
