Enthalpy & Heat. Flashcards
What is Energy?
The capacity to supply heat or do work
What is w?
Work: quantity of energy transferred from one system to another relating to mechanical energery. EX: a change in volume against a pressure. Measured in J
How to type ∆?
opt J
What is q?
q is the measure of Heat in J
Genereally a measure of all heat in & out of a system.
∆U
The change in internal energy of a system.
∆U=q (+/-) w
1st law of thermodynamics: that defines the relationship between work and heat
ºF to ºC
(ºF)-32*5/9
ºF to K
Convert to ºC then add 273.15
ºC to K
Add 273.15
K to ºC
Subtract 273.15 K
ºC to ºF
(ºC)*9/5 +32
Relationship between enthalpy and entropy.
∆G=∆H-T∆S
What is H?
Enthalpy- the Measure of heat within a system, usually written as ∆H to determine the change of energy within a chemical reaction, since H on it’s own if very difficult to measure. typically measured in STP
What is Kc
The ratio of equilibrium between the products and the reactants at equlibrium.
How to Calculate Kc
Products/ Reactants.
What does a Large Kc Mean?
There are more products than reactants at equilibrium.
What does Kc less than 1 Mean?
There are more Reactants than products at equilibrium.
What is Q?
The reaction quotient this is calculated the same way as K
Q<K?
Reaction will shift towards the Products- Forward reaction.
Q>K?
Reactions Will shift towards the reactants- Reverse Reaction.
Enthalpy Equation?
H= U+PV
U?
Internal energy of a system.
H>0?
Endothermic- absorbs heat
H<0?
Exothermic- Releases heat.
STP
P: 1 ATM or Bar, T: 273.15 K/ 0ºC
Standard State Conditions:
P: 1 ATM or Bar, T: 298K/ 25ºC
How to calculate enthalpy using Chemical Equations?
∆H= the sum of the products - the sum of the reactants.
Cs?
Specific heat capacity at a constant pressure.
Why is ∆H=mCs∆T
Most ∆H are done at a constant pressure, making the ∆P=0 and there there PV=0 so it just leaves U/q
What is Entropy?
The measure of disorder within a system. A high entropy will have a lot of disorder and a low entropy will have less disorder.
What is G (Gibbs)
The measure of spontaneity/ free energy within a system. this is related by entropy and enthalpy.
∆S?
The change of entropy within a system.
-∆G
Spontaneous
+∆G
Non-Spontaneous.
How to calculate ∆S(surroundings)?
∆S= (-1)∆H/T
(T is in K)
If ∆H (-) & ∆S (+)?
The reactions will always be spontaneous.
If ∆H (+) & ∆S (-)?
The reaction will never be spontaneous.
If ∆H (+) & ∆S (+)?
The reaction will be spontaneous at high temperatures.
If ∆H (-) & ∆S (-)?
The reaction will be spontaneous at low temperatures.
What Happens when you add heat to an endothermic reversible reaction?
The reaction will shift towards products.
