The 1995 Nobel Prize in Chemistry was shared by Paul Crutzen, F. Sherwood Rowlan
ID: 869292 • Letter: T
Question
The 1995 Nobel Prize in Chemistry was shared by Paul Crutzen, F. Sherwood Rowland, and Mario Molina for their work concerning the formation and decomposition of ozone in the stratosphere. Rowland and Molina hypothesized that chlorofluorocarbons (CFCs) in the stratosphere break down upon exposure to UV radiation, producing chlorine atoms. Chlorine was previously identified as a catalyst in the breakdown of ozone into oxygen gas. Using the enthalpy of reaction for two reactions with ozone, determine the enthalpy of reaction for the reaction of chlorine with ozone.
Using the enthalpy of reaction for two reactions with ozone, determine the enthalpy of reaction for the reaction of chlorine with ozone. ClO(g) + O3(g) rightarrow Cl(g) + 2Oz(g) deltaH = -122.8 kJ/mol 2O3(g) rightarrow 3O2(g) deltaH =--285.3 kJ/mol O3(g) + Cl(g) rightarrow ClO(g) + O2(g) deltaH = ?Explanation / Answer
ClO + O3 ----> Cl + 2O2 ; dHrxn1o = -122.8 kJ
2O3 ----> 3O2 ; dHrxn2o = -285.3 kJ
O3 + Cl ----> ClO + O2 ; dHrxn3o
As we can see, when we reverse the first reaction and add it to the second reaction, we get the third reaction.
We do the same with the dHrxno values as well to calculate dHrxn3o
Thus, dHrxn3o = (-dHrxn1o) + dHrxnr2o [ Here a -ve sign with dHrxn1o indicates the reversal of the reaction ]
= -(-122.8) + (-285.3) = -162.5 kJ
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