Thermodynamics

Question 1

Thermodynamic vs. Kinetically stable

Answer 1

In making reactions we always thrive to make the most stable compound this is how nature operates.

1. Thermodynamic: deals with how stable the bond of a reactions are. When looking at thermodynamic we pay attention to delta G, temperature and entropy.
   
   1. A stable thermodynamic reaction means that the energy of the bonds in the products are more stable than the energy in the bond in the reactant. Quick way to measure that:
      
      1. Endothermic reaction: the bonds of the product has more energy than that of the reactant therefore the reactions is thermodynamically unfavorable.
         
         1. Delta H is positive.
         2. Heat is part of the reactant to can help drive the reactions
      2. Exothermic reaction: there is more heat in the reactant then in the product, therfore the reaction is thermodynamically favorable.
         
         1. delta H is negative
         2. Heat is part of the product ( excess from reactants reaction)
   2. Kinetic energy in a reaction: focuses on the activation energy. The amount of energy that the reactant will need to form and intermediate. The lower that energy is the more kinetically favored the reation (think of enzymes)

Question 2

What is thermodynamic?

Answer 2

It is a branch of physics tha tdeals with heat and temperature and their relation with energy

Question 3

What are the three laws of thermodynamics?

Answer 3

1. energy is conserved, neither created nor destroyed
2. The univers prefers disorder ( high value of entropy energy- J/K)
   
   1. phases: solid less < liquids < gases ( universe favors gases)
3. At zero temperature a solid has an entropy of zero.

Question 4

What is the difference between enthalpy and heat?

Answer 4

1. Heat (q): helps to measure the energy flow from a system to another due to the temperature.
   
   1. know the equation of heat transfers.
2. Enthalpy: tells us the total heat added or loss in a system to run a reaction, helps analyze the stability of the product of the reaction via analyzing the heat of the bonds.
   
   1. + delta H : bonds of products are more stable than the product
   2. - delta H: bonds of the product are more stable than the reactions ( thermodynamically favor)

Question 5

What is endothermic vs. exothermic in term of stability?

Answer 5

1. Exothermic: heat is part of the product, this is indicative that the product is thermodynamically stable because the bond of the reactants had more energy than those of the products which allows the equation to go through.
2. Endothermic: Heat is part of the reactant therefore heat had to be added to the reaction in order for the reaction to go through. Not termodynamically stable

Question 6

What is Gibs free energy?

Answer 6

1. It is the energy that allows us to see if a reaction is favored by nature.
   
   1. • delta G: spontaneous
   2. • delta G: non- spontaneous
2. Based on the reaction you can determine which combination of enthalpy and entropy is needed to have an either spontaneous or non-spontaneous reaction.

Question 7

What is the activation energy ?

Answer 7

1. Gives us an insight into the kinetically favorability of the reaction.
   
   1. the lower the activation energy the more kinetically favorable the equation.
2. Express as activation energy complext - reactant energy.

Question 8

What is Hess law?

Answer 8

A way to the predict the energy release and absorbed by a reaction in order to avoid Explosion

3 Rules

1. A reaction writen in reverse ( A+ B- C turned into C= A+B)
   
   1. will have the same delta H except you want to add a - in front of the delta H
   2. If you multiply the molar quantities of the equation by a coefficent the delta H must also be multiply
   3. Equation can be manipulated as long as the delta H is correctly converted.

Question 9

What is the delta H of formation?

Answer 9

1. it is the enthalpy that comes from making one mole of a substance from it’s element at the standard stated and in it’s most stable allotrope ( stable state)
2. If the element is not in the standard states than the heat of formation is zero.

Question 10

What is bond dissociation energy?

Answer 10

1. The bond in a reaction can be use to find out the enthalpy of the reaction. ( see equations)
   
   1. measure heat: added to break bonds or
   2. heat release from bond formation.

Explanation of results

• zero: heat bond broken = bond formed
• +: endothermic bonds of product have more heat
• • : exothermic bonds of reactants have more heat.

Question 11

State the heat temp of these phase changes

1. Liquid to gas
2. Gas to liquid
3. solid to liquid
4. Solid to gas
5. gas to solid

Answer 11

1. endothermic delpta H + Entropy: +
2. exothermic delta H- Entropy: -
3. endothermic H+ Entropy: +
4. endothermic H + Entropy: +
5. exothermic H- Entropy +

Question 12

What is the heat of fusion? and heat of vaporization?

Answer 12

• Heat of Fusion: the amount of heat needed to melt or freeze a substance
• Heat of vaporozation: amoun of heat needed to vaporize or condense a substance

Question 13

Describe these terms used to descripe the state os fusion

1. Isothermal
2. Isobaric
3. isochoric
4. adiobatic

Answer 13

1.