Hess's Law Video Lessons

Concept:

# Problem: 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.1. ClO(g) + O3(g) → Cl(g) + 2 O2(g)            ΔHrxn = -122.8KJ/mol2. 2 O3(g) → 3 O2(g)                                 ΔHrxn = -285.3 KJ/mol3. O3(g) + Cl(g) → ClO(g) + O2(g)             ΔHrxn = ?

###### FREE Expert Solution

We can use Hess’s Law to determine the enthalpy change of the overall reaction from the given reactions:

1. ClO(g) + O3(g) → Cl(g) + 2 O2(g)            ΔHrxn = -122.8KJ/mol

2. 2 O3(g) → 3 O2(g)                                 ΔHrxn = -285.3 KJ/mol

3. O3(g) + Cl(g) → ClO(g) + O2(g)             ΔHrxn = ?

We now need to find a combination of reactions that when added up, gives us the overall reaction.

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###### Problem Details

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.

1. ClO(g) + O3(g) → Cl(g) + 2 O2(g)            ΔHrxn = -122.8KJ/mol

2. 2 O3(g) → 3 O2(g)                                 ΔHrxn = -285.3 KJ/mol

3. O3(g) + Cl(g) → ClO(g) + O2(g)             ΔHrxn = ?