Unit 1.4 Thermochemistry Flashcards
Unit 1: Physical Chemitry
What is Thermochemistry?
The study of the changes in energy that occur during chemical reactions
What is Thermodynamics?
The study of heat and tempeture and their relation to other forms of energy and work
What is the First Law of Thermodynamics?
The total energy of the universe is constant. Energy can neither be created nor destroyed. It can be converted from one form to another while the total energy remains the same
What is the Second Law of Thermodynamics?
The total entropy of a reaction system and its surroundings always increases for a spontaneous process.
What is a Spontaneous Reaction?
Is one that proceeds of its own accord
What is the Third Law of Theremodynamics?
The entropy of a perfect crystal at a tempeture of 0 kelvin is zero
What is Ethalpy?
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
What are Standard Conditions?
Tempeture- 298K
Pressure- 1 atmosphere
What is a Standard State of a Substance?
The most stable state of the substance under standard conditions
What is the Standard Enthalpy of Formation? (ΔHf)
The enthalpy when one mole of a substance is formed from its element in their standard states, it can be exothermic or endothermic
What is the Standard Enthalpy of a Reaction? (ΔHº)
The enthalpy change for reaction in which the reactants and products are in their standard states at a specified temp it can be calculated (data booklet)
What is Entropy? (S)
A measure of the degree of disorder of a system
When going from a solid to a gas what happens to the entropy?
Low entropy to a high entropy
What is the affect of changing tempeture on the entropy in a system?
As the tempeture increases the entropy increases
What is the affect of dissolving a solid on the entropy in a system?
This will cause a decrease in the entropy of the water, but a large increase in entropy of solute will result in a net gain in entropy
What is the affect of mixtures on the entropy in a system?
Mixtures have a greater entropy than pure substances. Diffusion causes no change in enthalpy, but does cause an increase in entropy
What is the affect of the number of moles on the entropy in a system?
Less moles - more order - lower entropy
More moles - more disorder - higher entropy
What is Standard Entropy? (S ∘)
The entropy of 1 mole of a substance in its standard state
What is an Spontaneous Exothermic Reaction?
Most spontaneous reactions are exothermic. The change in enthalpy is negative - energy is realsed so the products are more stable than the reactants
What is a Spontaneous Endothermic Reaction?
The enthalpy change is positive, so energy is taken in. Products have higher energy than reactants so are less stable
When is water freezing into ice spontaneous?
T<0c
When is ice melting into water spontaneous?
T>0c
What happens when Ice melts into Water?
System entropy increases. Endothermic - energy in to break bonds
What happens when Water freezes into Ice
System entropy decreases. Exothermic - energy out when bonds form
What is Gibbs Free Energy? (Δ G)
This is the energy that is available in a system to do work, it links to the enthalpy and entropy changes of the system
What is a Feasible/Spontaneous Reaction?
If the change in free energy between the reactants and products is negative, the reaction will proceed - it is feasible/spontaneous reaction
What happens if ΔG° < 0?
Its thermodynamically feasible and will proceed
What happens if ΔG° > 0?
Its not thermodynamically feasible and will not proceed
What happens if ΔG° = 0?
It is at equlibrium
