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Kassandra Molina 2B
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Joined: Wed Nov 16, 2016 3:03 am


Postby Kassandra Molina 2B » Tue Nov 28, 2017 8:42 pm

how do you get the sum of the first two reactions to equal the third reaction? asking from example in Chapter 11 pg 439.
Also why do we multiply the second reaction by a factor of 2?

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Joined: Sat Jul 22, 2017 3:01 am

Re: ICE Box

Postby skalvakota2H » Tue Nov 28, 2017 9:49 pm

The first equation has 2 molecules of PCl3 as product, while the second equation has 1 molecule of PCl3 as reactant. However, we notice that the third and final equation is the overall reaction, and PCl3 is neither a reactant nor product. Hence, this implies that PCl3 is an intermediate and must be cancelled out.
This means we must multiply the second equation by two in order to get 2 molecules of PCl3 as reactant.

Adding two chemical equations means cancelling moles of species that appear on opposite sides of the equations and combining moles of species that appear on the same sides of the equations.

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