Please show working out 1. a) Calculate the thermal energy released per mole of
ID: 884125 • Letter: P
Question
Please show working out
1. a) Calculate the thermal energy released per mole of reactants. Use the values shown and give the answer in kilojoules per mole by using the concentration and volume data given (calculate how many moles of ammonia or hydrochloric acid were used and then multiply the qreaction by the appropriate factor to obtain the answer in Joules and then convert to kiloJoules). One decimal place only for your answer. No units.
concentration of NH3 is 0.4 M and the volume is 250 mL
concentration of HCl is 2.0 M and the volume is 50 mL
qcontents = 310 J
qcalorimeter = 3869 J
qreaction = -4179 J
b) The thermal energy (-4179 J) that has warmed the calorimeter and contents has been converted from chemical energy in the reactants. Was the reaction A. exothermic or B. endothermic?
2. If qcontents = -1913J then the reaction is endothermic since qreaction = -(qcontents + qcalorimeter). Did energy flow A. from the calorimeter to its contents or B. from the contents to the calorimeter (qreaction is positive)? Think about this question! Type A or B as your answer.
3. Calculate the enthalpy change when ammonium chloride, NH4Cl(s), is dissolved in water, if qcontents was -1913J and qcalorimeter was -150J. Answer in Joules
qreaction = -(qcontents + qcalorimeter ) = ?
Explanation / Answer
1 a) moles of NH3 = 0.4 x 250 / 1000 = 0.1
moles of HCl = 2 x 50 / 1000 = 0.01
here limiting reagent is HCl . so 0.01 moles of NH3 consumed
Q reaction per mole = -4179 J
for 0.01 moles = -4179 x 0.01
= 41.79 J
= -0.04 kJ
so answer = -0.04 kJ
(b) answer : A. exothermic
(2) A. from the calorimeter to its contents
explanation : qreaction is positive . that means endothermic. hear transfer from calorimeter to content
(3) qreaction = -(qcontents + qcalorimeter )
= - (-1913 -150)
= 3063 J
enthalpy change = qreaction = 3063 J