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Delta H

Posted: Mon Jan 20, 2020 10:41 am
by Jessica Castellanos
When delta H is positive, is it endothermic or exothermic? And if H is negative?

Re: Delta H

Posted: Mon Jan 20, 2020 11:30 am
by Kevin Antony 2B
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.

Re: Delta H

Posted: Mon Jan 20, 2020 12:22 pm
by sarahforman_Dis2I
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.

Re: Delta H

Posted: Mon Jan 20, 2020 6:28 pm
by Hussain Chharawalla 1G
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.

Re: Delta H

Posted: Mon Jan 20, 2020 6:31 pm
by aishwarya_atmakuri
If delta H is negative, it is exothermic. If delta H is positive, it is endothermic.

Re: Delta H

Posted: Tue Jan 21, 2020 11:31 am
by Ashley Fang 2G
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.

Re: Delta H

Posted: Thu Jan 23, 2020 5:27 pm
by Caroline Beecher 2H
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).

Re: Delta H

Posted: Thu Jan 23, 2020 5:36 pm
by Jialun Chen 4F
I agree with Caroline's answer. If positive Delta H, endothermic; if negative Delta H, exothermic.

Re: Delta H

Posted: Fri Jan 24, 2020 9:12 am
by Sean Cheah 1E
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.

Re: Delta H

Posted: Fri Jan 24, 2020 1:25 pm
by Michellekim1H
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).

Re: Delta H

Posted: Fri Jan 24, 2020 1:42 pm
by Elizabeth Harty 1A
positive delta H means endothermic, negative delta H means exothermic.