A student decides to find the molar enthalpy for the reaction between phosphoric acid and calcium hydroxide. They have a 0.250 M solution of Ca(OH)2, which they will use; they can only find a 2.9 M stock solution of H3PO4. If they want 200 mL of a 0.31 M solution of H3PO4, how many mL of the stock solution should they use to prepare their solution by diluting the stock? Give your answer to the nearest mL.
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
![**Problem Statement:**
A student decides to find the molar enthalpy for the reaction between phosphoric acid and calcium hydroxide. They have a 0.250 M solution of Ca(OH)₂, which they will use; they can only find a 2.9 M stock solution of H₃PO₄. If they want 200 mL of a 0.31 M solution of H₃PO₄, how many mL of the stock solution should they use to prepare their solution by diluting the stock?
Give your answer to the nearest mL.
**Solution Explanation:**
To solve this problem, the student needs to use the dilution equation:
\[ C_1V_1 = C_2V_2 \]
Where:
- \( C_1 \) = concentration of the stock solution (2.9 M)
- \( V_1 \) = volume of the stock solution needed
- \( C_2 \) = concentration of the diluted solution (0.31 M)
- \( V_2 \) = volume of the diluted solution (200 mL)
Rearrange the formula to solve for \( V_1 \):
\[ V_1 = \frac{C_2V_2}{C_1} \]
Plug in the known values:
\[ V_1 = \frac{0.31 \times 200}{2.9} \]
Calculate \( V_1 \):
\[ V_1 ≈ 21.38 \, \text{mL} \]
Round to the nearest mL:
\[ V_1 = 21 \, \text{mL} \]
Therefore, the student should use 21 mL of the stock solution to prepare the 0.31 M solution.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Feac4d301-280e-44a9-9b77-05aa59bdadf8%2F836ec240-e345-4812-adb3-6dced8ef61aa%2Fd2mlymj_processed.png&w=3840&q=75)
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