In a coffee-cup calorimeter, 1 mol NaOH and 1 mol HBr initially at 28 oC (Celsius) are mixed in 100g of water to yield the following reaction: NaOH + HBr → Na+(aq) + Br-(aq) + H2O(l) After mixing the temperature rises to 88.5 oC. Calculate the change in enthalpy of this reaction. Specific heat of the solution = 4.184 J/(g oC) State your answer in kJ with 3 significant figures. Don't forget to enter the unit behind the numerical answer. The molecular weight of NaOH is 40.0 g/mol, and the molecular weight of HBr is 80.9 g/mol. ΔH =

The enthalpy change during the reaction is -56.0 kJ/mole.

Explanation:

Mass of 1 mole of NaOH = 40.0 g

Mass of 1 mole of HBr = 80.9 g

Mass of water = 100 g

Mass of solution ,m = 100 g + 40.0 g + 80.9 g = 220.9 g

First we have to calculate the heat gained by the solution.

where,

m = mass of solution

q = heat gained = ?

c = specific heat =

= final temperature =

= initial temperature =

Now put all the given values in the above formula, we get:

 ( J = 0.001 kJ)

Now we have to calculate the enthalpy change during the reaction.

where,

= enthalpy change = ?

q = heat gained = 23.4 kJ

n = number of moles NaOH = 1 mole

Therefore, the enthalpy change during the reaction is -56.0 kJ/mole.

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