Elemental carbon usually exists in one of two forms: graphite or diamond. It is

Question

Elemental carbon usually exists in one of two forms: graphite or diamond. It is generally believed that diamonds last forever. Here are the standard enthalpy of formation (delta ) and the standard molar entropy (S degree) values for diamond and graphite. What is the standard Gibbs free energy for the transformation of diamond to graphite at 298 K? Cdiamond Cgraphite Express your answer to three significant figures and include the appropriate units. part of the reaction. The general thermodynamic formula that is used to predict the spontaneity of a chemical reaction is the Gibbs free energy, defined as follows: is the standard change in free energy from the reaction, delta is the standard change of enthalpy (heat flow) in the reaction, T is the temperature in kelvins, and delta is the standard change in entropy (disorder) during the reaction. If delta is negative for a given reaction, it means that there will be a net flow of free energy from the reacting system into the environment, and the reaction is favored thermodynamically. Such a reaction is said to be spontaneous. Be aware, however, that spontaneous does not mean instantaneous, and that thermodynamically favored reactions may still occur very slowly. For example, the hydrogenation of ethene, H2C=CH2, to form ethane, H3C-CH3, is a thermodynamically favored reaction for which delta = -125 kJ/mol. However, when hydrogen gas, H2, and ethene are mixed together at room temperature, they react spontaneously, but at a rate so slow as to be undetectable. The reaction between carbon tetrachloride, CCI4, and water, H20, to form carbon dioxide, C02, and hydrogen chloride, HCl, has a delta value of - 232 kJ/mole, and so is thermodynamically favored. But when you mix carbon tetrachloride with water, no change is observed. What is a possible explanation for this? The reaction is not favored thermodynamically. It is a slow reaction kinetically. The activation energy of the reaction is too small. The reaction is not spontaneous. You have some propene , H2C=CHCH3, in a compressed gas tank that you need to convert to propane, H3CCH2CH3, to run your cabin heater and fridge. You have another tank of compressed hydrogen gas, H2, sitting out in your shed. Your first idea is to fill up a third tank with a mixture of the two gases, but when you try that, nothing happens. You look under your kitchen sink and find some powdered palladium mixed in inert charcoal. You take the palladium and put it into the flowpath from the hydrogen and propene tanks. As you begin flowing the mixture of propene and hydrogen, you notice with glee that by the time the gas reaches the receiving tank, it is propane gas. After all the propene has been converted to propane, you pour the palladium-charcoal mixture into a crucible. After analyzing the palladium, you notice that its chemical state has not changed. What word best describes the role that the palladium plays in the reaction between propene and hydrogen above? It is a catalyst. It is an activation energy barrier. It is a solvent. It is a reagent. What did the palladium do to to increase the rate of the reaction between the propene and hydrogen? It changed the thermodynamic equilibrium. It made the Gibbs free energy of the reaction more positive. It lowered the activation energy of the reaction. It increased the activation energy of the reaction.

Explanation / Answer

a) -2.898 KJ/mol
b) The reaction is slow kinetically.

c) It acts as a catalyst.

d) It lowers the activation energy barrier of the reaction.

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