Q=m(c∆t +heat of fusion + heat of evaporation)

m= 44g
c= 4.186 J/g.C
∆t= 107-(-8) =115 C
heat of fusion= 333.55 J/g
heat of evaporation=2260 J/g

Q=44(4.186*115 + 333.55 + 2260)
Q= 135297.36 J

5 0

3 years ago

Just enough 0.500 M HCl is added to 30.0 mL of 2.5 M NH3 to reach the equivalence point. The Kb of NH3 = 1.8 X 10-5

algol13

a.NH₃+HCl⇒NH₄Cl

b.volume HCl=150 ml

c. pH=4.82

<h3>Further explanation</h3>

Reaction

NH₃+HCl⇒NH₄Cl

The equivalence point⇒mol NH₃=HCl

Titration formula :

M₁V₁n₁=M₂V₂n₂(n=acid base valence, NH₃=HCl=1)

mol NH₃

$\tt 2.5\times 30=75~mlmol$

mol HCl=75 mlmol

Volume HCl :

$\tt \dfrac{75}{0.5}=150~ml$

Volume total :

$\tt 150+30=180~ml$

molarity of salt(NH₄Cl)

mol NH₄Cl=mol NH₃=75 mlmol=0.075 mol

$\tt M=\dfrac{0.075}{0.180}= 0.42$

pH of solution

Dissociation of NH₄Cl at water to find [H₃O⁺]

$\tt NH_4+H_2O\rightarrow NH_3+H_3O^+$

ICE at equilibrium :

0.41-x x x

Ka(Kw:Kb)= 10⁻¹⁴ : 1.8.10⁻⁵=5.6.10⁻¹⁰

$\tt Ka=\dfrac{NH_3.H_3O}{NH_4}=\dfrac{x^2}{0.41}$

[H₃O⁺]=x :

$\tt \sqrt{5.6.10^{-10}\times 0.41}=1.515.10^{-5}$

pH=-log[H₃O⁺]

$\tt pH=5-log~1.515=4.82$

7 0

3 years ago

Measurements show that the enthalpy of a mixture of gaseous reactants increases by 186.kJ during a certain chemical reaction, wh

pshichka [43]

To begin with, as Delta H = variation in enthalpy is >0 , it means rxn is endothermic.
The rule says: Delta U = Delta H + W = 186 -179 = 7 kJ.
Where Delta U is variation in internal energy and W is the work done.

7 0

3 years ago