Reaction Feasibility Flashcards
What is the standard enthalpy of formation, (ΔH°f) ?
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 a pressure of 1 atmosphere and at a specified temperature, usually taken as 298K.
How can you calculate the standard enthalpy of a reaction?
By using its Standard enthalpies of formation of the product and reactions using the formula sheet
What is the Entropy (S) of a system?
A measure of the degree of disorder of the system.
How does the degree of disorder impact the entropy?
The greater the degree of disorder, the greater the entropy.
Which have a higher value of (S) solids, liquids or gasses?
Solids have a low disorder and gases have a higher disorder.
How does temperature affect entropy?
Entropy increases as temperature increases.
What happens to the entropy of a substance at its melting and boiling points?
There is a rapid increase in entropy at the melting point of a substance and an even more rapid, larger change in entropy at the boiling point
What is the second law of thermodynamics?
The total entropy of a reaction system and its surroundings always increase for a spontaneous process.
How does the heat energy released by the reaction system impact the surroundings?
It increases the entropy of the surroundings.
When heat energy is absorbed from the surroundings by the reaction system, how does this affect their entropy?
The entropy of the surroundings decreases.
What is the third law of thermodynamics?
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.
What is the change in the free energy for a reaction related to?
The enthalpy and entropy changes
What does it mean if the free energy change (ΔG°) is negative?
The reaction is feasible
Does a feasible reaction tend towards the products or the reactants?
A feasible reaction tends towards the products.
How can you predict the feasibility for a reaction under standard conditions?
By calculating the standard free energy change (ΔG°)
How can you estimate what temperatures at which the reaction may be feasible?
By considering the range of values of T for which ΔG°<0
Under non-standard conditions any reaction if feasible if…
ΔG is negative
What does ΔG equal at equilibrium
Zero
A reversible reaction will proceed spontaneously until the composition is reached where…
ΔG=0
