Finals Flashcards
What is measured at constant pressure using a calorimeter?
delta H
Third Law of Thermodynamics
the entropy of a pure, perfectly crystalline substance at absolute zero (0K) is zero
Which are state functions and path functions?
state function: T, E, H, S, G, p, V, m, composition
path function: t,w and q
A reaction has a molar enthalpy (delta H) of formation of 50.63 kJ/mol. Under what conditions are the signs of delta E, w and q for this reaction?
*endothermic reaction
delta E = negative
w = negative
q = negative
How would you order the most stable to least stable to thermally decompose their elements under standard state conditions?
- Entropy (S)
1) most to least stable: solid, liquid, gas
2) bigger the molar mass, the less stable it is
First Law of Thermodynamics
Energy may be transferred as work or heat, but no energy can be lost, nor can heat or work be obtained from nothing
Second Law of Thermodynamics
There is an increase in entropy (disorder) as a spontaneous reaction occur in the universe; some energy lost as heat
The delta T is dependent on:
on the amount of heat transferred, q
on the direction of heat flow
inversely on the amount of material
on the identity of the material.
Heat capacity (C)
quantity of energy required to increase the temperature of a sample by 1°C
C is dependent on:
- mass of substance
- type of material
- state
- temperature
Specific heat capacity (Cs)
amount of heat energy required to raise the temperature of one g of a substance by 1°C
Jg-1K-1
Work (w)
energy used to move an object against an opposing force
w is dependent on:
- magnitude of the applied force
- displacement distance
As T increases, what happens to delta G
increases
Bond energy
energy required to break or make a bond
bond making= negative delta E
bond breaking= positive delta E
Exothermic vs Endothermic
Exothermic:if the reaction releases heat. Endothermic: if the reaction absorbs heat.
Enthalpy (delta H)
heat transferred into or out of a system at constant pressure.
Heat of vaporization
heat required to convert liquid to gas
Hess’s Law
A change in any state function is independent of path.
Thus, the energy change in a chemical reaction is independent of the manner in which the reaction takes place.
The enthalpy change for any overall process is equal to the sum of enthalpy changes for any set of steps that leads from the starting materials to the products.
Standard state
most stable form of a substance at T = 25 °C and p = 1 bar, and 1 M if it is in solution
delta H is dependent on:
temperature, concentration and pressure
Spontaneous direction
- preferred direction of reaction under specific conditions
- can only be reversed by the action of an outside force
What is the general tendency of heat?
Heat flows from high temperature to low temperature
Entropy (delta S)
the quantitative measure of dispersal resulting from an energy transfer
units: JK-1 or JK-1mol-1