Finding Molar Heat of a Solution

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In summary, the conversation discusses a lab experiment involving finding the Molar Heat in kJ/mol of salt dissolved in water. The initial and final temperatures of the solution are recorded, and the specific heat of water is known. The procedure involves mixing the salt in water and taking the temperature again. The specific heat of NH4Cl is unknown and there is uncertainty about how to proceed with the experiment. The suggested solution is to make assumptions and use the heat capacity of water to approximate the Molar Heat of the solution.
  • #1
RevoLuTioN31
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Hello,

I am doing a lab currently where we are required to find the Molar Heat in kJ / mol of salt dissolved of the salt, NH4Cl

To start the experiment, I dissolved the salt into an amount of water (values below) and recorded temperature changes.

Mass of NH4Cl = .9 g
Mass of H2O = 23.5 g (mL of water as well)
Temperature initial of Water = 21°C
Temperature final of Solution = 19°C

Procedure: I placed the 23.5 mL of water in a styrofoam cup, took the temperature and then added the salt. I mixed the salt around and took the temperature again at it's lowest point. I know the specific heat of water is 4.186 J / g°C. I do not know the specific heat of NH4Cl.

I am unsure where to go from here. Do I find the specific heat of NH4Cl online and then solve for its temperature initial? Am I doing the experiment wrong or is there another experiment to find the Molar Heat of the Solution (defined to me as the amount of heat given or taken from the salt)? :confused: Thanks for the help.
 
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  • #2
Since you've not been instructed to measure an initial temperature for sal ammoniac, you are faced with a necessity/ies to make assumptions; assumption a) could be that the final solution is dilute enough that its heat capacity is equal to that of water, and ΔHsol'n = 24.4 x 4.186 x 10-3 kJ x 2.00 /(0.9 mol/53.5).
 
  • #3
1. compute how many moles n of NH4Cl you have
2. Compute the heat lost by the water
3. answer = C ΔT/n
where C = water heat capacity.
This is approximate & assumes mass of solute << mass of solvent.
This is chemistry a field in which I'm no expert so take it with the proverbial grain of NaCl.
 

1. What is the purpose of finding the molar heat of a solution?

The purpose of finding the molar heat of a solution is to determine the amount of heat that is absorbed or released when a certain amount of solute is dissolved in a solvent. This can help us understand the thermodynamics of a solution and how it will behave under different temperature conditions.

2. How is the molar heat of a solution calculated?

The molar heat of a solution is calculated by dividing the heat released or absorbed by the number of moles of solute dissolved in the solution. This gives us the heat energy per mole of solute, which is expressed in units of joules per mole (J/mol).

3. What factors can affect the molar heat of a solution?

Several factors can affect the molar heat of a solution, including the nature and amount of solute and solvent, the temperature of the solution, and any changes in pressure or volume during the dissolution process.

4. How does the molar heat of a solution differ from the specific heat of a substance?

The molar heat of a solution specifically refers to the heat energy involved in dissolving a solute in a solvent, while the specific heat of a substance is the amount of heat required to raise the temperature of a given amount of that substance by 1 degree Celsius. The molar heat of a solution takes into account the heat involved in both the dissolution and the change in temperature of the solution.

5. What are some applications of knowing the molar heat of a solution?

Knowing the molar heat of a solution can be useful in various applications, such as understanding the thermodynamics of chemical reactions and processes, designing and optimizing industrial processes, and predicting and controlling changes in temperature during a chemical reaction. It can also help in determining the concentration of a solution and in the development of new materials with specific thermal properties.

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