Question 8.105

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Niharika Reddy 1D
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Question 8.105

Postby Niharika Reddy 1D » Sat Jan 24, 2015 11:38 am

Question 8.105 states: Vehicle air bags protect passengers by allowing a chemical reaction to occur that generates gas rapidly. Such a reaction must be both spontaneous and and explosively fast. A common reaction is the decomposition of sodium azide, NaN3, to nitrogen gas and sodium metal.

For the subsequent questions, the solutions manual uses the reaction for the decomposition of NaN3 to nitrogen gas and sodium gas, which affects the calculations for the standard entropy of the reaction and thus the standard Gibbs free energy, as the molar entropy of sodium gas is 153.71 J/K mol whereas that of solid sodium metal is 51.21 J/K mol. Why does sodium metal mean sodium gas instead of solid? I understand that airbags need to generate gas rapidly but I used the thermodynamic data for solid sodium since the question says sodium metal is formed.

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Re: Question 8.105

Postby Chem_Mod » Mon Jan 26, 2015 7:38 pm

"A common reaction is the decomposition of sodium azide, NaN3, to nitrogen gas and sodium metal."
The term sodium metal means Na not Na+. All the metal elements with zero oxidation state are referred to as "metals".
In this reaction Na(g) is the product.

Agreed the question could be more clear that sodium metal gas is formed. Of course it would be very odd if one had Na(s) formed in an explosively fast reaction. Think about that, a metal solid being formed and shooting out towards the passenger to 'inflate' the air bag.

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