### Which Of The Following Is A Statement Of Hess’S Law?

Answer and Explanation: 1 – Option a is the correct answer. Hess’s law is a result of the law of conservation of energy, which states that energy cannot be created nor destroyed in physical and chemical processes. As a result, if you start with the same reactants and produce the same products, the energy change will be the same regardless of the steps taken.

#### What is Hess’s law Short answer?

Solved Example – Question: Calculate the standard enthalpy change for a reaction CO 2 (g) + H 2 (g) → CO(g) + H 2 O(g) Given that Δ r H o for CO2(g), CO(g) and H 2 O(g) as -393.5, -110.5 and 241.8kJ/mol respectively.

• Solution:
• Δ r H o for the reaction is given as
• Substituting the given values, we get
• = + 41.2 kJ

Hess’s law states that the increase in enthalpy in a chemical reaction i.e., reaction heat at constant pressure is independent of the process between the initial and final states. It generally refers to the idea that, inevitably, everything in the universe transitions from order to chaos, and entropy is the measure of that transition.

• The term entropy has its origins in Greek entropy, meaning “a change toward” or “transformation.” Hess’s law allows the enthalpy shift (even if it can not be determined directly) to be estimated for a reaction.
• This is achieved by carrying out simple algebraic operations based on the chemical equation of reactions using values previously defined for the formation of enthalpies.

The Hess’s law states that in a chemical reaction, the change of enthalpy (i.e. the heat of reaction under constant pressure) is independent of the direction between the original and final states. The law of Hess requires the change in enthalpy ( Δ H) for a reaction to be determined even though it can not be directly measured. Put your understanding of this concept to test by answering a few MCQs. Click ‘Start Quiz’ to begin! Select the correct answer and click on the “Finish” buttonCheck your score and answers at the end of the quiz Visit BYJU’S for all Chemistry related queries and study materials

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View Quiz Answers and Analysis : Hess’s Law (Constant Heat Summation) – Definition, Equation, Formula & Applications

#### Why is Hess law correct?

According to this, when a reaction is carried out in a series of steps, the total enthalpy change is equal to the sum of the individual step enthalpy changes according to the principle of energy conservation. Since enthalpy is a part of the state, the Hess law is correct.

### Why is Hess’s law used?

A representation of Hess’s law (where H represents enthalpy) Hess’s law of constant heat summation, also known simply as Hess’ law, is a relationship in physical chemistry named after Germain Hess, a Swiss -born Russian chemist and physician who published it in 1840.

The law states that the total enthalpy change during the complete course of a chemical reaction is independent of the sequence of steps taken. Hess’s law is now understood as an expression of the fact that the enthalpy of a chemical process is independent of the path taken from the initial to the final state (i.e.

enthalpy is a state function ). According to the first law of thermodynamics, the enthalpy change in a system due to a reaction at constant pressure is equal to the heat absorbed (or the negative of the heat released), which can be determined by calorimetry for many reactions.

• The values are usually stated for reactions with the same initial and final temperatures and pressures (while conditions are allowed to vary during the course of the reactions).
• Hess’s law can be used to determine the overall energy required for a chemical reaction that can be divided into synthetic steps that are individually easier to characterize.

This affords the compilation of standard enthalpies of formation, which may be used to predict the enthalpy change in complex syntheses.

### Who made the Hess law?

Germain Henri Hess
Germain Henri Hess
Born 7 August 1802 Geneva, Canton of Léman, Helvetic Republic
Died 13 December 1850 (aged 48) St. Petersburg, Russia
Nationality Russian – Swiss
Alma mater University of Dorpat
Known for Hess’s law, Thermochemistry
Scientific career
Fields Chemistry
Institutions St. Petersburg Academy of Sciences

Germain Henri Hess ( Russian :, romanized : German Ivanovich Gess ; 7 August 1802 – 30 November 1850) was a Swiss-Russian chemist and doctor who formulated Hess’s law, an early principle of thermochemistry,

## What is Hess’s law a level chemistry?

Energy changes occur in chemical reactions as bonds are broken and new bonds formed. Enthalpy changes can be calculated from experimental data, and are independent of the route taken (Hess’s Law).

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Hess’s Law states that the enthalpy change for a chemical reaction is independent of the route taken. This means that the enthalpy change for the overall process will be identical regardless of how many steps are taken. Consider the following reaction: \ The enthalpy change for the reaction that forms products C+D directly $$(\Delta H_ )$$ will be the same as the sum of the enthalpy changes for the production of C+D via an indirect route where intermediate products are formed and subsequently react to produce C+D. One method of calculating an enthalpy change for a process involves rearranging a set of given reaction equations with known values. The following points must be noted when manipulating equations:

• The enthalpy change for the process ( $$\Delta H$$ ) is independent of the route taken (This is Hess’s law).
• The enthalpy change ( $$\Delta H$$ ) is proportional to the quantities of reactants and products. For example, burning twice as much fuel will result in twice the enthalpy change for the process.
• If a reaction is reversed then the sign of the enthalpy change must also be reversed.
• Changing the physical state of any reactant (or product) will involve an enthalpy change.
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#### Is Hess’s law always true?

Hess’s law is true because it embodies the laws of thermodynamics.

## What is Hess Law Class 11 with example?

State Hess’s law of constant heat summation and explain it with an example. Answer Verified Hint: Before attempting this question, prior knowledge of Enthalpy is a must. Enthalpy is a thermodynamic quantity,equal to the sum of internal energy of the system and the product of pressure and volume $(H = U + pV)$.

Complete step by step solution: Hess’s law of constant heat summation-According to this law, the change in enthalpy for a reaction is always the same and does not depend on whether the reaction occurs in one step or multiple steps. ORThe Hess’s law states that the total enthalpy change during a complete chemical reaction is the same regardless of the path taken by the chemical reaction.

ORThis law states that, the change in enthalpy in a chemical reaction, at a constant pressure is not dependent on the process, and only dependent on the initial and final states of the chemical reaction.It can be more easily understood by the following diagram. Hess’s law can be seen as an application of the principle of conservation of energy.As enthalpy only depends upon the initial and final state of the chemical reaction, it is also considered as a state function.Example:-Consider the following two routes for preparation of methylene chloride\ from the reaction between methane$(C )$ and chlorine$(C )$Route I:$C (g) + 2C (g) \to C C (g) + 2HCl(g),\Delta H_1^0 = – 202.3kJ$Route II:$C (g) + C (g) \to C Cl(g) + HCl(g),\Delta H_2^0 = – 98.3kJ \\ C Cl(g) + C (g) \to C C (g) + HCl(g),\Delta H_3^2 = – 104.0kJ \\$Adding change in enthalpy of both steps$C (g) + 2C (g) \to C C (g) + 2HCl(g),\Delta H_3^0 = – 202.3kJ$Thus, it can be clearly seen that no matter what path we follow, the total enthalpy change in the reaction is always the same.$\Delta H_1^0 = \Delta H_2^0 + \Delta H_3^2 = – 202.3kJ$Note: Hess’s law is named after Germain Hess, a Russian chemist who was born in Switzerland.

#### How do I verify Hess law?

Finally, to verify Hess’s Law, you will use the H’s you measured for the first two reactions to calculate H for the third reaction. Compare it to what you measured for the third reaction by calculating the Percent Error.

#### How do you use Hess’s law for enthalpy change?

Hess’s Law, also known as “Hess’s Law of Constant Heat Summation,” states that the total enthalpy of a chemical reaction is the sum of the enthalpy changes for the steps of the reaction. Therefore, you can find enthalpy change by breaking a reaction into component steps that have known enthalpy values.

#### Is Hess law conservation of energy?

Hess’s Law is based on the conservation of energy. The conservation of energy states that energy is not lost or gained but only changed in form.

## What is Hess law Toppr?

Hess’s law of constant heat summation: The law states that the change in enthalpy for a reaction is the same whether the reaction takes place in one or a series of steps. The Hess’s law can also be stated as the enthalpy change for a chemical reaction is the same regardless of the path by which the reaction occurs.

### Who made the Hess law?

Germain Henri Hess
Germain Henri Hess
Born 7 August 1802 Geneva, Canton of Léman, Helvetic Republic
Died 13 December 1850 (aged 48) St. Petersburg, Russia
Nationality Russian – Swiss
Alma mater University of Dorpat
Known for Hess’s law, Thermochemistry
Scientific career
Fields Chemistry
Institutions St. Petersburg Academy of Sciences

Germain Henri Hess ( Russian :, romanized : German Ivanovich Gess ; 7 August 1802 – 30 November 1850) was a Swiss-Russian chemist and doctor who formulated Hess’s law, an early principle of thermochemistry,

### What is Hess law Quizizz?

Hess’s Law states that all reactions are reversible. the enthalpy change of a reaction is independent of the route taken. the direct route results in a greater enthalpy change. the indirect route results in a lower enthalpy change as energy is lost in the second step.