Delta H

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Jessica Castellanos
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Delta H

Postby Jessica Castellanos » Mon Jan 20, 2020 10:41 am

When delta H is positive, is it endothermic or exothermic? And if H is negative?

Kevin Antony 2B
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Re: Delta H

Postby Kevin Antony 2B » Mon Jan 20, 2020 11:30 am

To see if something is endothermic r exothermic we look at delta G. If delta G is positive, the reaction is endothermic, but if it is negative the reaction is exothermic.

sarahforman_Dis2I
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Re: Delta H

Postby sarahforman_Dis2I » Mon Jan 20, 2020 12:22 pm

Jessica Castellanos wrote:When delta H is positive, is it endothermic or exothermic? And if H is negative?


If delta H is positive, that means the sum of the enthalpy of reactants is LARGER than the sum of the enthalpy of products. This means that the reaction is endothermic, or uses heat.

If delta H is negative, the sum of the enthalpy of reactants is SMALLER than the sum of the enthalpy of products. This means that the reaction is exothermic, or releases heat. Dr. Lavelle said that we will go more in depth about delta H, delta G and delta S later in the quarter.

Hussain Chharawalla 1G
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Re: Delta H

Postby Hussain Chharawalla 1G » Mon Jan 20, 2020 6:28 pm

If it helps, another way to think of delta H or enthalpy is the energy stored in bonds. If the products are in a lower energy more stable configuration, the reaction will be exothermic.

aishwarya_atmakuri
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Re: Delta H

Postby aishwarya_atmakuri » Mon Jan 20, 2020 6:31 pm

If delta H is negative, it is exothermic. If delta H is positive, it is endothermic.

Ashley Fang 2G
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Re: Delta H

Postby Ashley Fang 2G » Tue Jan 21, 2020 11:31 am

sarahforman_Dis2I wrote:
Jessica Castellanos wrote:When delta H is positive, is it endothermic or exothermic? And if H is negative?


If delta H is positive, that means the sum of the enthalpy of reactants is LARGER than the sum of the enthalpy of products. This means that the reaction is endothermic, or uses heat.

If delta H is negative, the sum of the enthalpy of reactants is SMALLER than the sum of the enthalpy of products. This means that the reaction is exothermic, or releases heat. Dr. Lavelle said that we will go more in depth about delta H, delta G and delta S later in the quarter.


I believe you switched it the other way, the idea is enthalpy of products - enthalpy of reactants = delta H
But yes, positive delta H means endothermic, negative delta H means exothermic.

Caroline Beecher 2H
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Re: Delta H

Postby Caroline Beecher 2H » Thu Jan 23, 2020 5:27 pm

The rule of thumb is that when delta H is positive, it is endothermic (it takes up heat and its' surroundings become cooler) and when delta H is negative, it is exothermic (it releases heat and its' surroundings become warmer).

Jialun Chen 4F
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Re: Delta H

Postby Jialun Chen 4F » Thu Jan 23, 2020 5:36 pm

I agree with Caroline's answer. If positive Delta H, endothermic; if negative Delta H, exothermic.

Sean Cheah 1E
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Re: Delta H

Postby Sean Cheah 1E » Fri Jan 24, 2020 9:12 am

Kevin Antony 2B wrote:To see if something is endothermic r exothermic we look at delta G. If delta G is positive, the reaction is endothermic, but if it is negative the reaction is exothermic.

When determining whether a reaction is exothermic/endothermic, one should look at the sign of delta H (change in enthalpy). The sign of G tells you whether a given reaction is exergonic/endergonic, which sounds similar but is completely different.

Michellekim1H
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Re: Delta H

Postby Michellekim1H » Fri Jan 24, 2020 1:25 pm

Positive delta H is endothermic(since there’s more energy in the products) whereas negative delta H is exothermic(there’s less energy in the products).

Elizabeth Harty 1A
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Re: Delta H

Postby Elizabeth Harty 1A » Fri Jan 24, 2020 1:42 pm

positive delta H means endothermic, negative delta H means exothermic.


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