Introduction
Understanding Gibbs free energy changes is crucial for determining the spontaneity of chemical reactions. In this article, we will explore how changes in enthalpy ( Delta H ) and entropy ( Delta S ) influence whether a reaction occurs spontaneously. We will examine three different reactions, analyze their thermodynamic properties, and determine their spontaneity at various temperatures.
The Basics of Gibbs Free Energy
Gibbs free energy ( Delta G ) provides a useful criterion for assessing the spontaneity of chemical processes. According to the Gibbs free energy equation:
[ Delta G = Delta H - T * Delta S ]
Where:
- (Delta G) is the change in Gibbs free energy,
- (Delta H) is the standard enthalpy change,
- T is the absolute temperature (in Kelvin), and
- (Delta S) is the standard entropy change.
Spontaneity Criteria
A reaction is said to be spontaneous if:
- (Delta G < 0)
Reaction Analysis
Reaction 1: Dissolution of HCl Gas in Water
- Reaction: HCl(g) → HCl(aq)
- Enthalpy Change (Delta H): Negative (exothermic)
- Entropy Change (Delta S): Negative
Here, we have fewer gaseous particles in the product than in the reactant, indicating a decrease in entropy.- Conclusion: At all temperatures, this reaction is not spontaneous due to negative (Delta G), which may become only negative at low temperatures.
Reaction 2: Decomposition of Ammonia
- Reaction: 2NH₃(g) → N₂(g) + 3H₂(g)
- Enthalpy Change (Delta H): Positive (endothermic)
- Entropy Change (Delta S): Positive
The entropy increases as the number of gaseous products (4 moles) exceeds that of the gaseous reactant (2 moles).- Conclusion: This reaction is not spontaneous at all temperatures and requires high temperatures for spontaneity. Here, the positive entropy makes (Delta G) negative when T is sufficiently high.
Reaction 3: Formation of HCl Gas
- Reaction: H₂(g) + Cl₂(g) → 2HCl(g)
- Enthalpy Change (Delta H): Negative
- Entropy Change (Delta S): Positive
The production of gas leads to an increase in entropy.
- Conclusion: This reaction is spontaneous at all temperatures due to both negative (Delta H) and positive (Delta S).
Summary
In summary, the spontaneity of chemical reactions can be evaluated using Gibbs free energy changes involving enthalpy and entropy. In the discussed reactions, we have seen that:
- The dissolution of HCl gas is non-spontaneous at all temperatures.
- The decomposition of ammonia is non-spontaneous at low temperatures but can become spontaneous at high temperatures.
- The formation of HCl gas is spontaneous at all temperatures due to favorable thermodynamic properties.
This understanding of Gibbs free energy can help clarify the conditions required for reaction spontaneity in various chemical processes.
so now that you're familiar with the Gibs free energy change and how it helps us determine if a reaction is
spontaneous or not let's solve this question to see if you've really understood this concept you see as
simple as this concept is there are times when students do get confused with the signs of the various thermodynamic
functions that are involved here like Delta H not or Delta s not and if you two get confused at these signs then
solving this question might just help you with the same okay so let's look at the question it says which of the
following reactions is spontaneous at all temperatures so the reactions are given to us and we also have information
on the Delta H not values which is the standard enthalpy changes for these reactions now we can figure out if these
reactions are spontaneous or not using the Gibs equation which is Delta g r is equal to Delta HR minus t Delta s not R
which is the standard GS free energy change is equal to the standard enthalpy change of the Rea action minus
temperature here T is for temperature multiplied by Delta s notr which is the standard entropy change for the reaction
and Delta s not values we can predict if the Delta G for these reactions would be negative and whether they would be
spontaneous or not okay so the first reaction here is a dissolution reaction where HCL gas is getting dissolved in
water to form aquous CL now this reaction is exothermic and releases a lot of heat as you can see from the
Delta H value it is negative here we now need to look at the entropy Factor by looking at this equation we can see that
we have more number of gaseous particles in the reactant site as compared to the product side correct we have a gaseous
reactant and an aquous product so that means in this case the entropy is decreasing and because the system
changes from a more chaotic and Freer gous state to a more ordered aquous State there is a net decrease in entropy
the entropy change in this reaction would be negative so for this reaction both Delta H and Delta s are negative so
clearly you can see that this reaction will not be spontaneous at all temperatures in fact to make this
reaction spontaneous we have to keep a very low temperature so that the contribution from the T Delta s can be
minimized because what happens when we have higher temperature T Delta is not would become much larger and as a result
it can significantly overcome or overcompensate the negative enthalpy change resulting in a positive Delta G
therefore by keeping a low temperature we ensure that the enthalpy Factor becomes more dominant and helps make the
Delta G not negative and the reaction spontaneous all right so let's look at the second reaction which is the
decomposition of ammonia now in this case the Delta H value is positive that is the reaction
is endothermic so Delta H not here is positive and what can you predict about the Delta H not value for that let's
look at the reaction equation okay here you can see that there are fewer number of moles of gaseous reactants as
compared to the number of moles of gaseous products that means in this reaction the entropy increases and as a
result the Delta s not value would be positive now a positive entropy change is definitely preferable because that
would ensure that this entire term would become more negative and might help contribute to a negative Delta G not but
basically needless to say that this reaction is again not spontaneous at all temperatures and to make this reaction
spontaneous we need a very high temperature by increasing the temperature this entire term of minus t
Delta s not become sufficiently negative and can outweigh the positive enthalpy contribution and help make the Delta G
not for this reaction negative so in the decomposition of ammonia the reaction becomes spontaneous or Delta G not
becomes negative only at high temperature all right let's look at the last reaction so here again we have a
negative Delta H value and what about the Delta s value to determine the sign of Delta s not we again simply need to
look at the number of moles of gaseous products versus the number of moles of gaseous reactants as you can see in the
reactant side we do not have any gaseous component whereas the product side has four moles of gaseous HCL as we know
gases have much more positive entropy as compared to liquids and solids and that means the Delta s not value or the
change in entropy for this reaction is also positive now this is exceeding ly comfortable because in this case the
Delta G not value will be negative at all temperatures that Delta H is negative and a positive Delta s ensures
that this term is also negative and that contributes to a negative Delta G not making this reaction spontaneous at all
Heads up!
This summary and transcript were automatically generated using AI with the Free YouTube Transcript Summary Tool by LunaNotes.
Generate a summary for freeRelated Summaries
Understanding Enthalpy and Spontaneity in Chemical Reactions
Dive into the relationship between enthalpy, entropy, and spontaneity in chemical reactions in this comprehensive guide.
Understanding Spontaneous Reactions: Exploring Gibbs Free Energy with Methane
Learn how to determine if a methane reaction is spontaneous using Gibbs free energy calculations.
Calculating Standard Gibbs Free Energy Change for Chemical Reactions
Learn how to calculate the standard Gibbs free energy change for various chemical reactions step-by-step.
Understanding Delta-G and Equilibrium Constants in Chemical Reactions
Explore the relationship between delta-G, equilibrium constants, and spontaneity in chemical reactions.
Understanding Gibbs Free Energy: The Key to Exergonic and Endergonic Reactions
Explore the significance of Gibbs Free Energy in determining spontaneous reactions, including exergonic and endergonic processes in biochemistry.
Most Viewed Summaries
Pamamaraan ng Pagtamo ng Kasarinlan sa Timog Silangang Asya: Isang Pagsusuri
Alamin ang mga pamamaraan ng mga bansa sa Timog Silangang Asya tungo sa kasarinlan at kung paano umusbong ang nasyonalismo sa rehiyon.
Kolonyalismo at Imperyalismo: Ang Kasaysayan ng Pagsakop sa Pilipinas
Tuklasin ang kasaysayan ng kolonyalismo at imperyalismo sa Pilipinas sa pamamagitan ni Ferdinand Magellan.
A Comprehensive Guide to Using Stable Diffusion Forge UI
Explore the Stable Diffusion Forge UI, customizable settings, models, and more to enhance your image generation experience.
Pamaraan at Patakarang Kolonyal ng mga Espanyol sa Pilipinas
Tuklasin ang mga pamamaraan at patakarang kolonyal ng mga Espanyol sa Pilipinas at ang mga epekto nito sa mga Pilipino.
Imperyalismong Kanluranin: Unang at Ikalawang Yugto ng Pananakop
Tuklasin ang kasaysayan ng imperyalismong Kanluranin at mga yugto nito mula sa unang explorasyon hanggang sa mataas na imperyalismo.
If you found this summary useful, consider buying us a coffee. It would help us a lot!