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23 Nov 2019

A sample of 1 mol of gas initially at 1 atm and 298 k is heatedatconstant pressure to 350 K, then the gas is compressedisothermallyto its initial volume and finaly it is cooled to 298 Kat constantvolume. Which of the following values is zero?

a.) Change in entropy (surrounding) and change in Gibbsfreeenergy
b.) Change in entropy (system) and change inentropy(surrounding)
c.) q and w
d.) W
e.) Change in Gibbs free energy and change in entropy(system)

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Elin HesselLv2

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Photosynthesis is the process by which plants effectively capture energy from the sun and store it for later use by organisms. It's the fundamental process that enables the entire food chain. Actual photosynthesis is a highly complex process involving many steps and many different chemicals, but we can get an idea of what's happening to thermodynamic quantities (enthalpy, Gibbs free energy, and entropy) using simpler reactions.

Let's consider a toy model in which an input of energy (for example from the sun) is be used to combine water and carbon dioxide to create an organic molecule (formaldehyde) and oxygen, effectively "storing" that energy for use later. The simplest possible such process is given by:

CO₂ + H₂O â O₂ + CH₂O

The table lists the enthalpy of formation, ÎH_f and the entropy S for 1 mol of each of the substances involved in this reaction at 298 K and 10⁵ Pa.

	ÎH_f (kJ)	S (kJ/K)
CH₂O	-115.9	0.2189
H₂O	-241.82	0.1888
CO₂	-393.51	0.2138
O₂	0	0.2051

Answer the following questions assuming that 1 mol of formaldehyde molecules are formed.

1. What is the change in enthalpy of this reaction?
ÎH = ____ kJ

Does this change in enthalpy represent energy that must be added to the system, or energy that is released from the system?
-Energy must be added or Energy is released?

2. What is the change in entropy for this reaction?
ÎS = ____ kJ/K

Does the entropy increase or decrease?
-Entropy increases or Entropy decreases?

At 298 K, what is the heat transfer that corresponds to this change in entropy?
Q = ____ kJ
Does this heat transfer represent energy that is added to the system, or energy that is released from the system?
--Energy is added Energy is released ?

3. What is the change in Gibbs free energy for this reaction?
ÎG = _____ kJ

The Gibbs free energies of formation, ÎG_f, are: -228.57 kJ for water; -394.36 kJ for CO₂; and 0 kJ for O₂. What is the Gibbs free energy of formation for formaldehyde?
ÎG_f (formaldehyde) = _______ kJ

4. Using the formation of formaldehyde as a model, comment on photosynthesis and the formation of sugars using what we know about entropy and free energy.

For a gaseous reaction, standard conditions are 298 K and a partial pressure of 1 atm for all species.

2NO(g)+O2->2NO2(g)

For the reactionthe standard change in Gibbs free energy is ÎGÂ° = -69.0 kJ/mol. What is ÎG for this reaction at 298 K when the partial pressures are

P NO: .350 atm P O2: .500 atm

PNO2: .700 atm

delta G in kj/mol

The molar enthalpy of fusion of solid cadmium is 6.11 kJ mol^-1, and the molar entropy of fusion is 10.3 J K^-1mol^-1.

(a) Calculate the Gibbs free energy change for the melting of 1.00 mol of cadmium at 566 K.

(b) Calculate the Gibbs free energy change for the conversion of 3.23 mol of solid cadmium to liquid cadmium at 566 K.

(c) Will cadmium melt spontaneously at 566 K? _____YesNo

(d) At what temperature are solid and liquid cadmium in equilibrium at a pressure of 1 atm?

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