When you combine 50.0 mL of 0.100 M AgNO3 with 50.0 mL of 0.100 M HCl in a coffee-cup calorimeter, the temperature changes from 23.40 °C to 24.21 °C. Calculate ΔHrxn for the reaction as written. Use 1.00 g/mL as the density of the solution and C = 4.18 J/g ∙ °C as the specific heat capacity.

Respuesta :

Answer : The enthalpy of reaction [tex](\Delta H_{rxn})[/tex] is, 67.716 KJ/mole

Explanation :

First we have to calculate the moles of [tex]AgNO_3[/tex] and [tex]HCl[/tex].

[tex]\text{Moles of }AgNO_3=\text{Molarity of }AgNO_3\times \text{Volume}=(0.100mole/L)\times (0.05L)=0.005mole[/tex]

[tex]\text{Moles of }HCl=\text{Molarity of }HCl\times \text{Volume}=(0.100mole/L)\times (0.05L)=0.005mole[/tex]

Now we have to calculate the moles of AgCl formed.

The balanced chemical reaction will be,

[tex]AgNO_3(aq)+HCl(aq)\rightarrow AgCl(s)+HNO_3(aq)[/tex]

As, 1 mole of [tex]AgNO_3[/tex] react with 1 mole of [tex]HCl[/tex] to give 1 mole of [tex]AgCl[/tex]

So, 0.005 mole of [tex]AgNO_3[/tex] react with 0.005 mole of [tex]HCl[/tex] to give 1 mole of [tex]AgCl[/tex]

The moles of AgCl formed  = 0.005 mole

Total volume of the solution = 50.0 ml + 50.0 ml = 100.0 ml

Now we have to calculate the mass of solution.

Mass of the solution = Density of the solution × Volume of the solution

Mass of the solution = 1.00 g/ml × 100.0 ml = 100 g

Now we have to calculate the heat.

[tex]q=m\times C\Delta T=m\times C \times (T_2-T_1)[/tex]

where,

q = heat

C = specific heat capacity = [tex]4.18J/g^oC[/tex]

m = mass = 100 g

[tex]T_2[/tex] = final temperature = [tex]24.21^oC[/tex]

[tex]T_1[/tex] = initial temperature = [tex]23.40^oC[/tex]

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

[tex]q=100g\times (4.18J/g^oC)\times (24.21-23.40)^oC[/tex]

[tex]q=338.58J[/tex]

Now  we have to calculate the enthalpy of the reaction.

[tex]\Delta H_{rxn}=\frac{q}{n}[/tex]

where,

[tex]\Delta H_{rxn}[/tex] = enthalpy of reaction = ?

q = heat of reaction = 338.58 J

n = moles of reaction = 0.005 mole

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

[tex]\Delta H_{rxn}=\frac{338.58J}{0.005mole}=6771.6J/mole=67.716KJ/mole[/tex]

Conversion used : (1 KJ = 1000 J)

Therefore, the enthalpy of reaction [tex](\Delta H_{rxn})[/tex] is, 67.716 KJ/mole

For this reaction, the heat of reaction is -67.8 KJ/mol.

The equation of the reaction is;

AgNO3(aq) + HCl(aq) -----> AgCl(s) + HNO3(aq)

Number of moles of AgNO3 = 50/1000 L ×  0.100 M = 0.005 M

Number of moles of HCl = 50/1000 L  ×  0.100 M = 0.005 M

Temperature change =  24.21 °C - 23.40 °C = 0.81°C

Total volume of solution =  50.0 mL +  50.0 mL = 100 mL

Since the density of solution= 1.00 g/mL

Total mass of solution = 100g

Heat absorbed by solution = mcθ

m = mass of solution

c = specific heat capacity of solution

θ = temperature change

Heat absorbed by solution = 100g ×  4.18 J/g ∙ °C  × 0.81°C = 0.339 KJ

ΔHrxn = -( 0.339 KJ)/ 0.005 M

ΔHrxn = -67.8 KJ/mol

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