# Calculate Molar Enthalpy of Hydrochloric Acid Solution

• Marzguerilla
He is right, though, in thinking that the mass of the solution is needed. The specific heat capacity of the solution would also be needed in order to get a final answer in joules.In summary, a laboratory technician added 43.1 mL of concentrated, 11.6 mol/L hydrochloric acid to water to form 500 ml of dilute solution. The temperature of the solution changed from 19.2C to 21.8C and the molar enthalpy of the equation is being calculated. Using the formula /\H=mc/\t/n, the mass of the solution was found to be approximately 500 grams. From there, the moles of HCl were calculated to be 1.
Marzguerilla

a laboratory technician adds 43.1 mL of concentrated, 11.6 mol/L hydrochloric acid to water to form 500 ml of dilute solution. the temperature of the solution changes from 19.2C to 21.8C. calculate the molar enthalpy of the equation.

so this is what is given
t=temperature (19.2-21.8= -2.6)
c=specific heat capacity. for water is 4.18 but i don't know if I am suppose water for this
m=mass I'm a bit lost in this one but i used 43.1ml/\H=mc/\t/n
this is what i tried

mHCl=43.1g t= -2.6 MHCl= 36.46 g/mol
43.1/36.46=1.18n mol
(43.1*4.18*-2.6)/ 1.182
=150.2

and i think the answer i got is wrong

Last edited:
For your change in temperature remember that it is the final temperature minus the initial temperature. You've shown the reverse. If the problem doesn't give you any information about the specific heat of the solution then it is probably safe to use 4.18 J/g-C. In reality, the specific heat of this solution would be slightly different. Mass is measured in grams...you are using milliliters. To find the mass of the solution, use the density of water (again, another assumption...assume density of solution is equal to that of water- 1.0g/mL unless otherwise stated).

umm yea i know to convert mL to gram. I still believe I am getting the wrong answer. i don't know what's up with the mass but I am thinking its not 43.1. I am so lost now :(

does anyone know how to do this question? I am praying to god that there was a mistake in my chemistry book

Marzguerilla said:

a laboratory technician adds 43.1 mL of concentrated, 11.6 mol/L hydrochloric acid to water to form 500 ml of dilute solution. the temperature of the solution changes from 19.2C to 21.8C. calculate the molar enthalpy of the equation.

so this is what is given
t=temperature (19.2-21.8= -2.6)
c=specific heat capacity. for water is 4.18 but i don't know if I am suppose water for this
m=mass I'm a bit lost in this one but i used 43.1ml

/\H=mc/\t/n

this is what i tried

mHCl=43.1g t= -2.6 MHCl= 36.46 g/mol
43.1/36.46=1.18n mol
(43.1*4.18*-2.6)/ 1.182
=150.2

and i think the answer i got is wrong

It's too bad that they don't give you the initial temperature of the HCl solution, but for the sake of solving the problem with respect how your instructor probably wants you to do it, we should neglect this important aspect of calculating the molar enthalpy

You need to use the 500 mL to calculate the mass of water

Use this to calculate "q"

Find the moles of HCl and divide the "q" by this value

Arrive at the final units of J of KJ / moles HCl

Marzguerilla said:
...
t=temperature (19.2-21.8= -2.6)
c=specific heat capacity. for water is 4.18 but i don't know if I am suppose water for this
m=mass I'm a bit lost in this one but i used 43.1ml

/\H=mc/\t/n

this is what i tried

m is the mass of the entire solution (assuming, as GCT pointed out, that the HCL is added at a temperature close to 19.2C). So that's the mass of about 543mL of liquid at a density of close to 1gm/mL.

Gokul43201 said:
m is the mass of the entire solution (assuming, as GCT pointed out, that the HCL is added at a temperature close to 19.2C). So that's the mass of about 543mL of liquid at a density of close to 1gm/mL.

The problem mentions "500 ml of dilute solution"; that is, 500 mL is the final volume right, unless I'm missing something here?

GCT said:
The problem mentions "500 ml of dilute solution"; that is, 500 mL is the final volume right, unless I'm missing something here?
No, you're right. I didn't read carefully. The mass involved is that of 500mL of solution.

## 1. What is molar enthalpy and why is it important?

Molar enthalpy, also known as molar heat of reaction, is a measure of the amount of heat released or absorbed during a chemical reaction per mole of reactant. It is important because it helps us understand the energy changes that occur during a chemical reaction, which is crucial in many industrial and scientific processes.

## 2. How is molar enthalpy calculated?

To calculate the molar enthalpy of a hydrochloric acid solution, we need to measure the change in temperature of the solution before and after the reaction, and the amount of hydrochloric acid used. We can then use the equation Q = mCΔT, where Q is the heat released or absorbed, m is the mass of the solution, C is the specific heat capacity of the solution, and ΔT is the change in temperature. We can then divide Q by the amount of hydrochloric acid used to get the molar enthalpy.

## 3. What factors can affect the molar enthalpy of a hydrochloric acid solution?

The concentration of the hydrochloric acid, the amount of acid used, the initial and final temperatures of the solution, and any impurities in the acid can affect the molar enthalpy of a hydrochloric acid solution. Other external factors, such as atmospheric pressure and humidity, can also have an impact on the molar enthalpy measurement.

## 4. How can the molar enthalpy of a hydrochloric acid solution be used in practical applications?

The molar enthalpy of a hydrochloric acid solution can be used to determine the amount of heat released or absorbed in various chemical reactions involving hydrochloric acid. This information is important in industries such as pharmaceuticals, where accurate control of heat energy is crucial for the production of medicines. It can also be used in the design and optimization of chemical processes and in the development of new materials.

## 5. Can the molar enthalpy of a hydrochloric acid solution ever be negative?

Yes, the molar enthalpy of a hydrochloric acid solution can be negative if heat is absorbed during the reaction. This can occur in endothermic reactions where energy is required to break bonds. In contrast, exothermic reactions release heat and have a positive molar enthalpy. The sign of the molar enthalpy is an indication of the direction of the reaction and the energy changes involved.

Replies
16
Views
2K
Replies
1
Views
31K
Replies
1
Views
2K
Replies
4
Views
2K
Replies
10
Views
6K
Replies
1
Views
4K
Replies
4
Views
3K
Replies
4
Views
39K
Replies
4
Views
33K
Replies
1
Views
9K