A student dissolves 10.6 g of potassium hydroxide KOHin 300. g of water in a well-insulated open cup. She then observes the temperature of the water rise from 22.0 °C to 29.2 °C over the course of 6.7 minutes.Use this data, and any information you need from the ALEKS Data resource, to answer the questions below about this reaction:→KOHs + K+aq OH−aqYou can make any reasonable assumptions about the physical properties of the solution. Be sure answers you calculate using measured data are rounded to the correct number of significant digits.Note for advanced students: it's possible the student did not do the experiment carefully, and the values you calculate may not be the same as the known and published values for this reaction.Is this reaction exothermic, endothermic, or neither? exothermicendothermicneitherIf you said the reaction was exothermic or endothermic, calculate the amount of heat that was released or absorbed by the reaction in this case. kJCalculate the reaction enthalpy ΔHrxn per mole of KOH. kJmol
Question
A student dissolves 10.6 g of potassium hydroxide KOHin 300. g of water in a well-insulated open cup. She then observes the temperature of the water rise from 22.0 °C to 29.2 °C over the course of 6.7 minutes.Use this data, and any information you need from the ALEKS Data resource, to answer the questions below about this reaction:→KOHs + K+aq OH−aqYou can make any reasonable assumptions about the physical properties of the solution. Be sure answers you calculate using measured data are rounded to the correct number of significant digits.Note for advanced students: it's possible the student did not do the experiment carefully, and the values you calculate may not be the same as the known and published values for this reaction.Is this reaction exothermic, endothermic, or neither? exothermicendothermicneitherIf you said the reaction was exothermic or endothermic, calculate the amount of heat that was released or absorbed by the reaction in this case. kJCalculate the reaction enthalpy ΔHrxn per mole of KOH. kJmol
Solution
The reaction is exothermic. This is because the temperature of the water increased, indicating that heat was released into the surroundings.
To calculate the amount of heat released, we can use the formula q = mcΔT, where m is the mass of the water, c is the specific heat capacity of water, and ΔT is the change in temperature.
Given: m = 300 g c = 4.18 J/g°C (specific heat capacity of water) ΔT = 29.2°C - 22.0°C = 7.2°C
Substituting these values into the formula, we get:
q = (300 g)(4.18 J/g°C)(7.2°C) = 9021.6 J
Since 1 kJ = 1000 J, we convert the heat to kJ:
q = 9021.6 J ÷ 1000 = 9.02 kJ
So, the amount of heat released by the reaction is approximately 9.02 kJ.
To calculate the reaction enthalpy ΔHrxn per mole of KOH, we first need to find the molar mass of KOH. The molar mass of K is approximately 39.1 g/mol, the molar mass of O is approximately 16.0 g/mol, and the molar mass of H is approximately 1.0 g/mol. Therefore, the molar mass of KOH is approximately 56.1 g/mol.
Given that 10.6 g of KOH was used in the reaction, the number of moles of KOH is:
n = 10.6 g ÷ 56.1 g/mol = 0.189 mol
The reaction enthalpy ΔHrxn per mole of KOH is then:
ΔHrxn = q ÷ n = 9.02 kJ ÷ 0.189 mol = 47.7 kJ/mol
So, the reaction enthalpy ΔHrxn per mole of KOH is approximately 47.7 kJ/mol.
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