# Heat of formation of nh4cl

• mullen1120
In summary, the conversation discusses a lab experiment involving a calorimeter and two reactions with ammonia and hydrochloric acid. The resulting deltaT values were 8.6 degC and -2.8 degC. The question at hand is how to calculate the deltaH per mole for each reaction. The first reaction is NH4+(aq) + Cl-(aq) ----> NH4Cl(aq) and the second reaction involves NH4Cl(s) dissolving in water. The heat capacity of the solution needs to be determined in order to accurately calculate the deltaH values.

## Homework Statement

i did a lab calorimeter lab with 50ml 1.51M nh3 and 50ml 1.59M hcl yeilding nh4cl (aq)
the deltaT was 8.6 degC
second part is 100ml of h2o and 4.082g nh4cl
deltaT was -2.8 degC

## Homework Equations

how do i find deltaH per mole for each reaction?

## The Attempt at a Solution

Hint: Write out the reactions for the first part and the second part. What form was the ammonia? Was it aqueous? How should that be written?

its nh3(aq) + hclz(aq) = nh4cl(aq)
and nh4cl(s) = nh4cl(aq)

but where do i go from there?

NH3 in water is NH4+ OH-
HCl in water is H3O+ Cl-

one of the two reactions is:

NH4+(aq) + Cl-(aq) ----> NH4Cl(aq)

Can you determine the other reaction?

You will need the heat capacity of the ammonium chloride solution. Can you determine what the concentration will be?
Alternatively, you could assume the heat capacity of pure water, but it won't be an exact solution. Can you think of why you need to obtain the heat capacity?

## 1. What is the heat of formation of NH4Cl?

The heat of formation of NH4Cl, also known as the enthalpy of formation, is the energy released or absorbed when one mole of NH4Cl is formed from its constituent elements in their standard states at a given temperature and pressure. It is represented by the symbol ΔHf and its value for NH4Cl is -314.4 kJ/mol.

## 2. How is the heat of formation of NH4Cl calculated?

The heat of formation of NH4Cl can be calculated using the Hess's Law, which states that the enthalpy change of a chemical reaction is independent of the pathway taken from reactants to products. The heat of formation is calculated by subtracting the enthalpies of formation of the reactants from the enthalpies of formation of the products, multiplied by their respective coefficients in the balanced chemical equation.

## 3. Why is the heat of formation of NH4Cl negative?

The negative sign in the value of the heat of formation of NH4Cl indicates that the reaction is exothermic, meaning that it releases heat. This is because the formation of NH4Cl from its constituent elements results in a more stable compound with lower energy than the individual elements.

## 4. How does temperature affect the heat of formation of NH4Cl?

The heat of formation of NH4Cl is dependent on temperature, as it is defined at a specific temperature and pressure. Changes in temperature can affect the energy required to break or form bonds, thus altering the enthalpy of formation. In general, the heat of formation increases with an increase in temperature.

## 5. What is the significance of the heat of formation of NH4Cl?

The heat of formation of NH4Cl is an important thermodynamic property that helps predict the energy changes in chemical reactions involving NH4Cl. It is also useful in determining the stability of a compound and its potential for use as a source of energy. Furthermore, the heat of formation is an essential parameter in the calculation of other thermodynamic properties, such as the heat of reaction and the standard enthalpy of formation.