Lecture 15- Thermodynamics 1

Question 1

Thermodynamics

Answer 1

• The relationship between chemical reactions and heat

- Temp= measure of thermal every and average KE of a sample

Question 2

Heat vs. temp

Answer 2

• Heat= a form of energy measured in Joules
• Temperature= a measure of average KE of atoms and molecules in a system
• 0K=no KE
• When KE doubles, K temp doubles

Question 3

Boltzmann Distribution and Temperature

Answer 3

• The greater distribution of KE of particles becomes more dispersed as temp increases and the average KE of particles in a system increases and temp increases
• Lower temp=smaller distribution of particles
• higher temp= wider distribution of particles
• Distribution of KE increases as temp increases
• Average KE of the particles in a system increases as temp increases

Question 4

Energy transfer between systems

Answer 4

• two systems at different temperatures that are in thermal contact with one another will exchange energy (heat)
• The energy transferred from system 1 is equal to the energy transferred to system 2
• shorter arrows= lower KE and V
• Longer arrows= higher KE and V

Question 5

system and surrounding

Answer 5

• system- the actual chemical reaction that is taking place

- surrounding- the entire universe outside of the chemical reaction

Question 6

change in a system’s internal energy

Answer 6

• ^E=q+w
• E= change in the PE and KE of the particles in a system
• q= heat that is transferred into (+value) or out of (-value) the system
• w= work done on the system by the surroundings (+ as energy flows into the system) or work done on the surrounding by the system (- value as energy flows out of the system)
• Work results from changes in the volume of a gas

Question 7

Heat and endothermic process

Answer 7

• pe+KE=PE+ke
• bonds in the products contain more PE, the product molecules contain less KE
• Products of an endothermic reaction are at a lower temperature
• heat flows from the surroundings into the system until thermal equilibrium is established

Question 8

Heat and exothermic processes

Answer 8

• ke+PE=KE+pe
• as the bonds in the products contain less PE, the product molecules must contain more KE
• This is why the products of an exothermic reaction are at a higher temperature
• heat flows from the system into the surroundings until thermal equilibrium is established

Question 9

Work and endothermic processes

Answer 9

• If the pressure caused by gas particles colliding with the piston on the outside of the cylinder is greater than that inside the cylinder… the has outside does work on the piston, energy is transferred from the gas to the piston, and the has inside the cylinder contracts. Big to small

Question 10

Work and exothermic process

Answer 10

• if the pressure caused by gas particles colliding with the piston on the inside of the cylinder is greater than that outside the cylinder, the gas inside does work on the piston, energy is transferred from the gas to the piston, and the inside the cylinder expands. Small to big

Question 11

Transfer of energy through work

Answer 11

• P=F/A
• F=PA
• w=F^d
• w=P^V
• w= -P^V***

Question 12

Enthalpy of Reaction (^H)

Answer 12

• the heat that is released or absorbed in a chemical reaction
• g-l is exothermic
• l-g is endothermic

Question 13

Four methods for finding ^H

Answer 13

1. average bond enthalpies
2. Calorimeter
3. Hess’s Law
4. Enthalpies of formation

Question 14

^H from average bond enthalpies

Answer 14

^H=sumBE(broken)-sumBE(formed)

• • is exothermic
• • is endothermic

Question 15

relating to gas

Answer 15

w= -P^V

Question 16

calculate the work associated with this contraction in joules

Answer 16

• w= -P^V
• gets you atmXL
• multiply by 101.3J/IatmL

Question 17

J/AtmL

Answer 17

101.3J/1atmL

Question 18

+ - W

Answer 18

-W=exothermic since energy is being released from the system
+W= endothermic since energy is being put into the system
- same for ^E

Question 19

calculate the change in internal energy of the balloon

Answer 19

• Use w= -P^V to find J

- Plug into ^E=q+w

Question 20

compare the sum of the bond enthalpies of reactants and the sum of the bond enthalpies of the products

Answer 20

• Use ^H=Hp-Hr for both the reactants the products (but just add)
• If sum of products is higher this means theres a higher KE and lower PE because its an exothermic reaction and more energy is released during the formation of bonds in the products that is required to break the bonds in the reactants and the products are at a lower PE than the reactants.

Question 21

determine enthalpy change ^Hrnx

Answer 21

^H=Hp-Hr

- elements are 0 since they don’t have bonds

Question 22

using average bond energies

Answer 22

^H=sumBE(broken)-sumBE(formed)

- reactants-products

Question 23

gas compressing

Answer 23

• positive= gas compressing

- negative= gas expanding