Question

When 50.0 mL of 1.00 M HCl and 50.0 mL of 1.00 M NaOH are mixed in a constant-pressure calorimeter, the temperature of the solution increases from 21.0°C to 27.5°C. Calculate the enthalpy change of the reaction per mole of HCl assuming the solution has a total volume of 100.0 mL and a density of 1.000 g/mL. The specific heat of water is 4.184 J/q°C Asoln = 2720

Answer 1

Given data,

Molarity of HCl= 1M

Molarity of NaOH=1M

Volume of HCl=50ml

Volume of NaOH=50ml

Therefore, number of moles of HCl and NaOH added can be found out by

n=MV / 1000

n= 1X50 / 1000 =0.05 moles

Also we can find the mass of the mixture from the equation

Mass= density X volume

Mass= 1x100= 100g [As from the given data total density=1.000g/l and total volume=100ml ]

Thus,the heat evolved in the reaction can be obtained from the equation

Heat evolved= mass of mixture X specific heat of water X change in temperature(T2-T1)

q=ms47

q= 100X4.184X(27.5-21.0)

q= 2719.6J =2.7196KJ

Finally, to find the enthalpy change of the reaction per mole is given by

Enthalpy change = Heat evolved in the reaction / number of moles of HCl

AH=
q / n

-2.7196 / 0.05 = -54.392 KJ

AH=

(In a constant pressure calorimeter eventhough it is insulated ,heat is transferred to the surroundings inside the calorimeter so we take the value of heat released which is taken to be exothermic enthalpy that is it becomes negative value )

Final Answer

AH= -54.392 KJ