A student dissolves 14.5 g of ammonium nitrate NH4NO3 in 250. g of water in a well-insulated open cup. She then observes the temperature of the water fall from 20.0 °C to 16.5 °C over the course of 8.1 minutes.Use this data, and any information you need from the ALEKS Data resource, to answer the questions below about this reaction:→NH4NO3s + NH+4aq NO−3aqYou 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 NH4NO3. kJmol
Question
A student dissolves 14.5 g of ammonium nitrate NH4NO3 in 250. g of water in a well-insulated open cup. She then observes the temperature of the water fall from 20.0 °C to 16.5 °C over the course of 8.1 minutes.Use this data, and any information you need from the ALEKS Data resource, to answer the questions below about this reaction:→NH4NO3s + NH+4aq NO−3aqYou 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 NH4NO3. kJmol
Solution
This reaction is endothermic. This is because the temperature of the water decreases when the ammonium nitrate is dissolved, indicating that heat is being absorbed from the water by the reaction.
To calculate the amount of heat absorbed by the reaction, 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.
The specific heat capacity of water is approximately 4.18 J/g°C. The mass of the water is 250 g, and the change in temperature is 20.0°C - 16.5°C = 3.5°C.
So, q = (250 g)(4.18 J/g°C)(3.5°C) = 3657.5 J = 3.6575 kJ (rounded to four decimal places).
To calculate the reaction enthalpy ΔHrxn per mole of NH4NO3, we need to know the molar mass of NH4NO3, which is approximately 80.04 g/mol.
The number of moles of NH4NO3 is 14.5 g / 80.04 g/mol = 0.1812 mol (rounded to four decimal places).
So, ΔHrxn = q / number of moles = 3.6575 kJ / 0.1812 mol = 20.17 kJ/mol (rounded to two decimal places).
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