Enthalpy of neutralization of phosphoric acid

The Enthalpy of Neutralization of Phosphoric Acid Worksheet

Describe coffee cup calorimetry and how it is used to find the enthalpy of various reactions that occur in aqueous solutions. Make sure to include the relevant equations. Why can you use the specific heat capacity and density of pure water to determine the enthalpy of reaction? What assumptions must be made in order to do this?

The reaction solution was prepared by mixing 50.0 ML of 0.60 M H3PO4 and 50.0 mL of 1.85 M NaOH. The reaction was carried out in a coffee cup and calculated the empathy of the reaction. It was assumed that, Styrofoam cup as an isolated system and energy lost to the surrounding was zero or negligible.

The energy change (q soln) in the system can be calculated by the following equation

qsol= Cs×m ×∆T

The qsol stands for the energy change, Cs is specific heat capacity of water and m represent the mass of the solution.

The energy change corresponding to the reaction can be defined by the following equation,

qrxn= -qsol

In the above equation –qrxn stands for the amount of the energy change of reaction.

Enthalpy of the reaction can be calculated by the following equation

∆H = qrxn/moles H3PO4

Enthalpy change per mole of the reaction solution can be calculated by the above equation.

Data: Insert your data table (with a caption) below that captures all of the relevant information.

Trial 1

Trial 2

Maximum Temperature oC

22.1

22.3

Initial Temperature oC

32.1

32.0

Temperature Change ∆T

10

9.7

Table: This table shows the change of temperature in the reaction.

Graph1: This graph for trial one that shows the change of Temp over Time of reaction

Results:

∆H=-139 KJ/Mol

Report your calculated average value of ∆H of neutralization for phosphoric acid. Include hand written sample calculations.

Percent Error= 12.3%

Report the percent error for the ∆H of neutralization for phosphoric acid. Include any calculations.

Discussion: Is your value for the ∆H of neutralization for phosphoric acid greater than or less than the accepted value. Think of some valid sources of error to account for your difference and explain how they would contribute to the direction of your error.

The value is less than the expected for the ∆H of neutralization for phosphoric acid. There were few random errors during the experiment. The main random error was not sealing the top of the coffee cup off. The system was left open. The cup was not closed and heat was lost to the surrounding. The system did not reach it is maximum temperature because heating was being lost constantly to the surrounding. The maximum temperature should been higher when the reaction was carried out. One way to avoid a random error like this one is by sealing off the top of the coffee cup. When you seal off the top of the coffee cop the heat will stay in the system and will not be lost to the surrounding.

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