Week 2 - CH/BI 126

Terms

100

In a reaction, if we form weaker bonds in the product, what is the reaction considered?

endothermic

200

Which of the following is an example of a state function?

a) length of time it takes to go from New York to Los Angeles

b) mileage travelled going from San Francisco to Los Angeles

c) amount of time it takes to change the channel

d) difference in altitude between Chicago and Denver

d

300

A chemical reaction where heat is transferred to the surroundings is an _____________ reaction

exothermic

400

If work is being added to the system, is work positive or negative from the perspective of the surroundings?

negative

500

What is the second law of thermodynamics?

The entropy of the universe always increases

Entropy

100

A reaction is spontaneous when the system has (negative or positive) entropy?

Positive

200

Which has the greater entropy, both systems have 5 particles in the ground state, 2 in the first excited state and 1 in the second excited state, but system A has smaller energy spacing than system B

neither, they have the same entropy

ways are the same, S=k*ln(W)

300

Calculate the change in entropy if a 8 moles of gas initially starts at 3.0 bar and becomes 1.3 bar

55.6 J/K

400

What is the change in entropy of the following reaction? (0.5 bar N2O4 and 7.3 bar NO2) 

N2O4 (g) → 2 NO2 (g) 

ΔrSo of N2O4 (g)= 304 J/mol K

ΔrSo of NO2 (g) = 240 J/mol K

ΔrSo= 176 J/mol K

If you account for the nonstandard pressure

ΔrS=137 J/mol K

This makes sense because entropy is increasing as the equation goes from one molecule of gas to two molecules of gas.

500

Calculate the change in entropy when (a) 250 mL of 12 M acetic acid is mixed with 750 mL of pure water. (b) 75.0 mL of 0.100M NaCl is mixed with 25.0 mL of 0.050 M MgBr2 

(a) 35 J/K

(b) 0.079 J/K

Internal Energy

100

A 12.8 g sample of ethanol (C₂H₅OH) is burned in a bomb calorimeter that has a heat capacity of 5.65 kJ/^oC. If the initial temperature is 25.0^oC, determine the final temperature of the calorimeter. The molar mass of ethanol is 46.07 g/mol.

C₂H₅OH_(l) + 3O_2(g)->2CO_2(g) + 2H₂O_(g) ∆H_rxn=-1235 kJ

85.7^oC

200

If the internal energy of a thermodynamic system is increased by 300 J while 75 J of expansion work is done, how much heat was transferred and in what direction (to or from the system)?

375 J

to the system

300

The volume of an ideal gas is decreased from 5.0 L to 2400.0 mL at a constant pressure of 2.0 atm. Calculate the work associated with this process in atmxL. Is work being done on the system or by the system?

5.2 atmxL

work being done on the system

400

A 35.6 g sample of ethanol (C2H5OH) is burned in a bomb calorimeter that has a heat capacity of 23.3 kJ/oC. If the temperature rose from 35.0oC to 76.0oC, what is the value of the heat of the reaction (∆H)?

-1240 kJ/mol

500

In a refrigerator system, the refrigerant gas absorbs 21.39 kJ of heat energy while expanding against a 0.278 atm pressure from a volume of 0.0423 L to a volume of 1.876 L. What is the energy change of the gas?

1L*atm=101.3 Joules

21338 J

Enthalpy

100

What is the standard enthalpy of fusion for Cl2(g), H2(g), and N2(g)?

All are 0

200

Under what condition is enthalpy equal to heat?

Constant Pressure

300

C3H8(g) + 5O2(g) --> 3CO2(g) +4 H20 (g)

The following list is the enthalpies of formation for the compounds:

ΔH C3H8=−103.85kJmol

ΔH CO2=−393.5kJmol

ΔH H2O=−241.82kJmol

If one mole of propane is burned, what is the enthalpy of the reaction?

−2044 kJ

400

3. Calculate the standard enthalpy change at 298 K for the reaction 

2CH4(g) --> C2H6(g) +H2(g)

C2H6=-83.14

Ch4= -74.81

64.94 kj/mol

500

 Determine the internal energy and enthalpy changes when 27.0 grams of boiling water are vaporized at an external pressure of 1 atmosphere after 61.5 kJ of energy has been added to the water.

Delta U=56.848 Kj

MISC

100

When power was turned off to a 30.0 gal water heater, the temperature of the water dropped from 75^oC to 22.5^oC. How much heat was lost to the surroundings? 

1 gal = 3.785 L

2.49 x 10⁷ J

200

Imagine a reaction where the reactants have a higher ground state than the products but smaller energy spacing. Will reactants or products dominate a low temperature? What about high temperatures?

Low temperatures - products

high temperatures - reactants

300

Calculate the delta rU for the reaction:

H2(g) +F2(g) --> 2HF(g)

H-H: 432

F-F: 154

H-F: 565

-544 kJ/mol

400

Calculate the value of H^o for the following reaction using the listed thermochemical equations:

P₄O_10(g) + 6PCl_5(g) ->10Cl₃PO_(g)

1/4 P_4(s) + 3/2Cl_2(g) -> PCl_3(g)      H^o = -306.4
P_4(s) + 5O_2(g) -> P₄O_10(g)     H^o= -2967.3
PCl_3(g) + Cl_2(g) -> PCl_5(g)    H^o = -84.2
PCl_3(g) + 1/2O_2(g) -> Cl₃PO_(g) H^o= -285.7

-610.1 kJ

500

Calculate the change in enthalpy at 298 K when 1 mole of glucose is combusted. 

Assuming the change in enthalpy for the combustion of glucose is the same at 37 C (the human body) as at 25 C, determine the amount of glucose in grams a person must consume to maintain an average daily input of 11.0 MJ for bodily function.

enthalpy of glucose:  -2802.04 kj/mol

grams of glucose needed = 706.6 grams