Steve, in an attempt to impress his girlfriend, plops 18.2 grams of sodium metal into 500 mL of concentrated phosphoric acid (density = 1.88 g/cm3) in a beaker. The reactants were both initially at 25 oC. The reaction gently produced bubbles of hydrogen and Janet was not impressed. What was the final temperature of the reaction mixture if all the heat is transferred to/from the phosphoric acid?

Question

Steve, in an attempt to impress his girlfriend, plops 18.2 grams of sodium metal into 500 mL of concentrated phosphoric acid (density = 1.88 g/cm3) in a beaker. The reactants were both initially at 25 oC. The reaction gently produced bubbles of hydrogen and Janet was not impressed. What was the final temperature of the reaction mixture if all the heat is transferred to/from the phosphoric acid?

2 H3PO4 (l) + 6 Na (s) = 2 Na3PO4 (s) + 3 H2 (g)
Thermodynamic data for phosphoric acid can be found on the National Institutes of Standards and Technology website:
webbook.nist.gov/cgi/cbook.cgi?ID=C7664382&Mask=2&Type=JANAFL&Table=on#JANAFL).

Answer 1

To determine the final temperature of the reaction mixture, we need to calculate the heat transfer between the reaction and phosphoric acid.

First, we need to determine the amount of heat released or absorbed during the reaction. This can be done using the heat of reaction, which can be found using the thermodynamic data provided in the National Institutes of Standards and Technology (NIST) website.

Using the given balanced equation:
2 H3PO4 (l) + 6 Na (s) → 2 Na3PO4 (s) + 3 H2 (g)

The heat of reaction, ΔH, is the amount of heat released or absorbed when the reaction proceeds as written. The heat of reaction can be calculated by taking the difference in the standard enthalpy of formation between the products and reactants.

However, the NIST website does not provide the heat of reaction directly. Instead, we need to use the standard enthalpy of formation values for the compounds involved and apply the Hess's Law to calculate the heat of reaction.

Hess's Law states that the sum of the enthalpy changes for a series of reactions is equal to the enthalpy change of the overall reaction. By using known reactions with known enthalpy changes, we can determine the enthalpy change of the desired reaction.

Unfortunately, the given information does not provide enough details about the standard enthalpy of formation values for the compounds involved. To calculate the heat of reaction, we need to know these values.

Therefore, without the specific enthalpy data, we cannot calculate the final temperature of the reaction mixture.