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### Test 2

Posted: Fri Mar 08, 2019 12:30 pm
Can someone please explain why Gibbs free energy for the combustion of a gas used to heat a BBQ at a pool party is negative? Wouldn't it require be a non-spontaneous process for the combustion to occur?

### Re: Test 2

Posted: Fri Mar 08, 2019 12:37 pm
The Gibbs free energy of the combustion of gas would be negative, as the reaction is exergonic. This is because gas will have more energy than the water and CO2 molecules released after the combustion, and thus the reaction will be spontaneous.

### Re: Test 2

Posted: Sun Mar 10, 2019 8:18 pm
If the Gibbs Free energy of a rxn is lees than zero, then that means it will occur spontaneously.

### Re: Test 2

Posted: Sun Mar 10, 2019 8:24 pm
What happens if Gibbs free energy is zero exactly?

### Re: Test 2

Posted: Sun Mar 10, 2019 8:28 pm
a negative gibbs free energy means it is spontaneous, unlike a negative entropy which means its nonspontaneous

### Re: Test 2

Posted: Sun Mar 10, 2019 9:37 pm
Carissa Young 1K wrote:What happens if Gibbs free energy is zero exactly?

When Gibbs free energy is zero, that means that the reaction is at equilibrium.

### Re: Test 2

Posted: Sun Mar 10, 2019 10:00 pm
Also if gibbs free energy is zero, the free energy of the reactants equals that of the products

### Re: Test 2

Posted: Sun Mar 10, 2019 10:01 pm
Since a combustion releases heat, you can therefore say that the reaction is exothermic and Gibbs free energy is negative

### Re: Test 2

Posted: Sun Mar 10, 2019 10:22 pm
Lauren Huang 1H wrote:Can someone please explain why Gibbs free energy for the combustion of a gas used to heat a BBQ at a pool party is negative? Wouldn't it require be a non-spontaneous process for the combustion to occur?

This question confused me as well. After the test, I realized it was spontaneous because combustion itself is spontaneous, as it releases heat. Yes, the BBQ needs heat, but the heat is provided by the heat released from the combustion reaction.

### Re: Test 2

Posted: Sun Mar 10, 2019 10:46 pm
Did anyone understand what delta G should be for the question from test 2 where it talks about photosynthesis of an old tree?

### Re: Test 2

Posted: Sun Mar 10, 2019 10:49 pm
Delta G would be less than zero because combustion releases heat and is spontaneous.

### Re: Test 2

Posted: Sun Mar 10, 2019 11:24 pm
delta G is negative as a combustion will increase the entropy S, or disorder, of the system and is therefore spontaneous.

### Re: Test 2

Posted: Sun Mar 10, 2019 11:38 pm
Delta G is negative because the reaction is exergonic.