Are exothermic reactions spontaneous?

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Discussion Overview

The discussion centers around the spontaneity of the exothermic reaction between potassium hydroxide (KOH) and sulfuric acid (H2SO4) to form potassium sulfate (K2SO4) and water (H2O). Participants explore the conditions under which this reaction occurs, its thermodynamic properties, and whether observable signs of spontaneity can be detected during the reaction.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant notes that the reaction is exothermic and questions its spontaneity, seeking clarification on how to determine this.
  • Another participant explains that spontaneity is determined by the Gibbs free energy change, emphasizing that not all exothermic reactions are spontaneous, using the example of freezing water.
  • A participant acknowledges the Gibbs free energy concept but expresses uncertainty about observing signs of spontaneity in their experiment.
  • There is a discussion about calculating the delta G value and whether the delta H value corresponds to the enthalpy of neutralization.
  • One participant provides a detailed explanation of spontaneity, defining conditions for spontaneous, non-spontaneous, and equilibrium states, and gives examples of various reactions to illustrate these concepts.
  • Examples include the spontaneous formation of water from hydrogen and oxygen, the exothermic reaction between KOH and H2SO4, and an endothermic reaction involving barium hydroxide and ammonium thiocyanate.
  • Another example is provided regarding the non-spontaneity of dissolving NaCl in water under standard conditions, despite being exothermic.

Areas of Agreement / Disagreement

Participants express differing views on the spontaneity of the reaction, with some asserting it is spontaneous under standard conditions while others highlight the complexity of defining spontaneity based on Gibbs free energy. The discussion remains unresolved regarding the visibility of spontaneous reactions and the specific conditions that affect spontaneity.

Contextual Notes

Participants reference specific concentrations of reactants and the conditions under which the reaction occurs, but there are unresolved questions about the visibility of the reaction and the exact parameters for determining spontaneity.

Who May Find This Useful

This discussion may be useful for students and researchers interested in thermodynamics, reaction kinetics, and the principles of chemical spontaneity in exothermic reactions.

PhyChemMath
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The reaction between
2KOH + H2SO4 -> K2SO4 + 2H2O
is exothermic...

However is this reaction spontaneous as well? If so then why?
the concentration that i used was:
KOH - 2M
H2SO4 - 1M


(I writting a lab report on the "course of this reaction"...spontaniety of the reaction is a part of my observation table...so if the reaction is spontaneous, will it be visible to naked eyes? )
 
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Hi PhyChemMath, welcome to PF. At constant temperature and pressure, spontaneity is determined by whether the Gibbs free energy change of the reaction is negative. Exothermic processes aren't always spontaneous; consider freezing, which is exothermic but definitely not spontaneous for water at temperatures about 0°C.
 
hey thanks!
yea i get the gibbs free energy concept but in this case it is the formation of salt...
we titerated KOH(25ml) with H2SO...adding 1ml of H2SO4 each time..


now i get what you are saying about whether not every exothermic reaction being spontaneous .. i didnt really see any visible signs of the reaction being spontaneous..

also if i were to calculate the delta G value i need a delta H value...will the delta H value be the enthalpy of neutralisation? ?
 
PhyChemMath said:
will the delta H value be the enthalpy of neutralisation?

Yes.
 
PhyChemMath said:
The reaction between
2KOH + H2SO4 -> K2SO4 + 2H2O
is exothermic...

However is this reaction spontaneous as well? If so then why?
the concentration that i used was:
KOH - 2M
H2SO4 - 1M


(I writting a lab report on the "course of this reaction"...spontaniety of the reaction is a part of my observation table...so if the reaction is spontaneous, will it be visible to naked eyes? )
Spontaneous means that it happens or that it would happen, in those thermodynamic conditions, if catalyzed. Non spontaneous means that it couldn't happen, in those thermodynamic conditions, even if catalyzed.
Spontaneous: DeltaG < 0.
Non spontaneous: DeltaG > 0.
Equilibrium: DeltaG = 0

Examples:
1) H2 + (1/2)O2 --> H2O
is spontaneous at standard conditions, but it doesn't happen, unless you catalyze it (example: a little spark).

2) 2KOH + H2SO4 --> K2SO4 + 2H2O
is spontaneous at standard conditions and it happens without other means. You can infer the fact it happens from temperature increase (for example) because this reaction is exothermic. If you are not convinced, try to use KOH 6M and H2SO4 6M (be careful).

3) 1g of ice at 0°C + 1litre of water at room temperature --> ice melts
is spontaneous and it happens, but it's not exothermic, it's endothermic.

4) Ba(OH)2*8H2O + 2NH4SCN --> Ba(SCN)2 + 2NH3 + 8H2O
is spontaneous and it happens, and it's endothermic at well:
http://www.youtube.com/watch?v=MyAzjSdc3Fc&feature=player_embedded#

5) A dilute solution of NaCl in water( standard conditions) --> NaCl(solid) + H2O is NOT spontaneous and infact it doesn't happen. If it happened it would be exothermic.
 

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