chemistry - unit 2.2 Flashcards
What is the standard enthalpy of formation?
The enthalpy change when one mole of a substance is formed from its elements in their standard states.
What is the standard state of a substance?
Its most stable state at a pressure of 1 atmosphere and at a specified temperature, usually taken as 298 K.
How can the standard enthalpy of a reaction be calculated?
From the standard enthalpies of formation of the reactants and products.
What is the entropy (S) of a system?
A measure of the degree of disorder of the system.
The greater the degree of disorder…
…the greater the entropy.
What have low disorder and what have high disorder?
Solids have low disorder and gases have high disorder.
When does entropy increase?
When temperature increases.
When is there a rapid increase in the entropy of a substance?
At its melting point and even a more rapid and larger change in entropy at the boiling point.
What does the second law of thermodynamics state?
The total entropy of a reaction system and its surroundings always increases for a spontaneous process.
What increases the entropy of the surroundings?
Heat energy released by the reaction system into the surroundings.
What decreases the entropy of the surroundings?
Heat energy absorbed by the reaction system from the surroundings.
What does the third law of thermodynamics state?
The entropy of a perfect crystal at 0K is zero.
What is the standard entropy of a substance?
The entropy value for the substance in its standard state.
If the change in free energy between reactants and products is negative, what may happen?
A reaction may occur and the reaction is said to be feasible.
What is a feasible reaction?
One that tends towards the products rather than the reactants. This does not give any indication of the rate of reaction.
