Understanding Hess Law: Enthalpy Summation vs. Heat Change in Chemical Reactions

In summary, the conversation discusses the concept of Hess Law, which states that the sum of all enthalpies of chemical reactions is constant. The question arises as to why only the sum of enthalpies is taken into consideration. The second part of the conversation brings up the difference between enthalpy and heat, and whether the concept of heat is valid in this context. The speaker then asks for clarification on the differences between thermodynamic and kinetic stability.
  • #1
syamdcs
1
0
You people heard about hess law means that sum of all enthalpies of chemical reactions takes place but why we only call sum of all enthalpies?

1)
A----B dH1
B----C dH2 HESS LAW
DH = dH1 + dH2

2)
A----B dQ1
B----C dQ2 ?
DQ = dQ1 + dQ2
In the above representations one is associated with enthapy and another is heat
whethe second one is valid or not?if so why?
 
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  • #2
Welcome to the forums syamdcs,

According to the rules of the forum, you must show your work/attempt before we can offer any assistance. Also, in future, could you please post homework questions in the appropriate forum. Thanks.
 
  • #3
please i will like u to give me some major diferences btw thermodynamic and kinetic stability
 

1. What is enthalpy and how does it relate to heat change?

Enthalpy is a thermodynamic quantity that represents the total amount of energy in a system. In the context of heat change, enthalpy measures the amount of heat absorbed or released during a chemical reaction or physical process. It is often denoted as ΔH, where Δ represents the change in enthalpy.

2. How is enthalpy calculated?

The change in enthalpy (ΔH) can be calculated using the formula: ΔH = H(products) - H(reactants), where H represents the enthalpy of the substance. This can also be expressed as the sum of the enthalpies of formation of the products minus the sum of the enthalpies of formation of the reactants.

3. What is an endothermic reaction and how does it affect enthalpy?

An endothermic reaction is a chemical reaction that absorbs heat from its surroundings. This type of reaction results in a positive change in enthalpy (ΔH>0), meaning that the system gains energy from the surroundings. This energy is often in the form of heat, hence the term "endothermic."

4. How does enthalpy relate to the first law of thermodynamics?

The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or converted. Enthalpy is a measure of the total energy in a system, and therefore, it is in accordance with the first law of thermodynamics. Any change in enthalpy reflects a transfer or conversion of energy within the system.

5. Can enthalpy be measured directly?

No, enthalpy cannot be measured directly as it is an abstract concept representing the total energy of a system. However, changes in enthalpy can be measured experimentally by measuring the amount of heat absorbed or released during a reaction using a calorimeter. This data can then be used to calculate the change in enthalpy for the reaction.

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