Changing sign of enthalpy

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Changing sign of enthalpy

Postby JulieAljamal1E » Sat Jan 26, 2019 12:12 am

When you have a chemical equation and you take the reverse reaction, why does delta H change sign to negative if it was originally positive and vice versa?

Harshita Talkad 4L
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Re: Changing sign of enthalpy

Postby Harshita Talkad 4L » Sat Jan 26, 2019 1:30 am

Since the positive and negative indicates whether energy is being absorbed or released for the reaction to take place, if the reaction absorbs heat in one direction, the reverse reaction will release heat since the bonds that were initially being broken are now being formed and vice versa.

Eunice Lee 1A
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Re: Changing sign of enthalpy

Postby Eunice Lee 1A » Sat Jan 26, 2019 12:57 pm

Since reversing the equation would reverse the chemical process taking place, the sign of the enthalpy would change. For example, if you start with an exothermic reaction, the enthalpy would be negative because the reactants are releasing/losing heat to form the products. If you reverse this reaction, the products going to the reactants would be an endothermic reaction. The enthalpy would then be positive because the products are gaining heat to form the reactants.

Emily Huang 1E
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Re: Changing sign of enthalpy

Postby Emily Huang 1E » Sat Jan 26, 2019 1:20 pm

It depends on whether the exothermic or endothermic reaction is favored. If the forward reaction is endothermic and is favored the delta H would be positive. If the reverse reaction is favored, the delta H becomes negative as the reverse reaction is exothermic.

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