A student dissolves 11.5 g of sodium chloride (NaCl)in 200. g of water in a well-insulated open cup. He then observes the temperature of the water fall from 22.0 °C to 20.1 °C over the course of 6.8 minutes. Use this data, and any information you need from the ALEKS Data resource, to answer the questions below about this reaction: NaCI(s) Na* (aq) + Cl¯ (aq) You can make any reasonable assumptions about the physical properties of the solution. Be sure answers you calculate using measured data are rounded to 2 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. O exothermic Is this reaction exothermic, endothermic, or neither? O endothermic O neither If you said the reaction was exothermic or endothermic, calculate the amount of heat that was released or absorbed by the reaction in this case. kJ Calculate the reaction enthalpy AH per mole of NaCl. rxn mol

A student dissolves 11.5 g of sodium chloride (NaCl)in 200. g of water in a well-insulated open cup. He then observes the temperature of the water fall from 22.0 °C to 20.1 °C over the course of 6.8 minutes. Use this data, and any information you need from the ALEKS Data resource, to answer the questions below about this reaction: NaCI(s) Na* (aq) + Cl¯ (aq) You can make any reasonable assumptions about the physical properties of the solution. Be sure answers you calculate using measured data are rounded to 2 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. O exothermic Is this reaction exothermic, endothermic, or neither? O endothermic O neither If you said the reaction was exothermic or endothermic, calculate the amount of heat that was released or absorbed by the reaction in this case. kJ Calculate the reaction enthalpy AH per mole of NaCl. rxn mol

Chemistry: The Molecular Science

5th Edition

ISBN:9781285199047

Author:John W. Moore, Conrad L. Stanitski

Publisher:John W. Moore, Conrad L. Stanitski

Chapter4: Energy And Chemical Reactions

Section: Chapter Questions

Problem 19QRT: Solid ammonium chloride is added to water in a beaker and dissolves. The beaker becomes cold to the...

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A piece of lead of mass 121.6 g was heated by an electrical coil. From the resistance of the coil, the current, and the Time the current flowed, it was calculated that 235 J of heat was added to the lead. The temperature of the lead rose from 20.4C to 35.5C. What is the specific heat of the lead?
The decomposition of ozone, O3, to oxygen, O2, is an exothermic reaction. What is the sign of q? If you were to touch a flask in which ozone is decomposing to oxygen, would you expect the flask to feel warm or cool?
A 50-mL solution of a dilute AgNO3 solution is added to 100 mL of a base solution in a coffee-cup calorimeter. As Ag2O(s) precipitates, the temperature of the solution increases from 23.78 C to 25.19 C. Assuming that the mixture has the same specific heat as water and a mass of 150 g, calculate the heat q. Is the precipitation reaction exothermic or endothermic?
Solid ammonium chloride is added to water in a beaker and dissolves. The beaker becomes cold to the touch. Make an appropriate choice of system and surroundings and describe it unambiguously. Explain why you chose the system and surroundings you did. Identify transfers of energy and material into and out of the system that would be important for you to monitor in your study. Is the process of dissolving NH4Cl(s) in water exothermic or endothermic? Explain your answer.
The specific heat capacity of copper is 0.385 J g1 C1, whereas it is 0.128 J g1 C1 for gold. Assume you place 100. g of each metal, originally at 25 C, in a boiling water bath at 100 C. If energy is transferred to each metal at the same rate, determine which piece of metal will reach 100 C first.
In a coffee-cup calorimeter, 1.60 g NH4NO3 is mixed with 75.0 g water at an initial temperature of 25.00C. After dissolution of the salt, the final temperature of the calorimeter contents is 23.34C. Assuming the solution has a heat capacity of 4.18 J/C g and assuming no heat loss to the calorimeter, calculate the enthalpy change for the dissolution of NH4NO3 in units of kJ/mol.
When 7.11 g NH4NO3 is added to 100 mL water, the temperature of the calorimeter contents decreases from 22.1 C to 17.1 C. Assuming that the mixture has the same specific heat as water and a mass of 107 g, calculate the heat q. Is the dissolution of ammonium nitrate exothermic or endothermic?
The formation of aluminum oxide from its elements is highly exothermic. If 2.70 g Al metal is burned in pure O2 to give A12O3, calculate how much thermal energy is evolved in the process (at constant pressure).
The process of dissolving ammonium nitrate, NH4NO3, in water is an endothermic process. What is the sign of q? If you were to add some ammonium nitrate to water in a flask, would you expect the flask to feel warm or cool?
As the gas trapped in a cylinder with a movable piston cools, 1.34 kJ of work is done on the gas by the surroundings. If the gas is at a constant pressure of 1.33 105 Pa, what is the change of volume (in L) of the gas?
When solid iron burns in oxygen gas (at constant pressure) to produce Fe2O3(s), 1651 kJ of heat is released for every 4 mol of iron burned. How much heat is released when 10.3 g Fe2O3(s) is produced (at constant pressure)? What additional information would you need to calculate the heat released to produce this much Fe2O3(s) if you burned iron in ozone gas, O3(g), instead of O2(g)?
Magnesium sulfate is often used in first-aid hot packs, giving off heat when dissolved in water. A coffee-cup calorimeter at 25C contains 15.0 mL of water at 25C. A 2.00-g sample of MgSO4 is dissolved in the water and 1.51 kJ of heat are evolved. (You can make the following assumptions about the solution: volume=15.0 mL, density=1.00 g/mL, specific heat=4.18J/gC.) (a) Write a balanced equation for the solution process. (b) Is the process exothermic? (c) What is qH2O? (d) What is the final temperature of the solution? (e) What are the initial and final temperatures in F?

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