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mr_godi [17]
3 years ago
11

When 1 mole of H2(g) reacts with F2(g) to form HF(g) according to the following equation, 542 kJ of energy are evolved H2(g) + F

2(g2HF(g) Is this reaction endothermic or exothermic? What is the value of q?
Chemistry
1 answer:
topjm [15]3 years ago
7 0

Answer: The reaction is exothermic. The value of q is  -542 kJ.

Explanation:

Endothermic reactions are defined as the reactions in which energy of the product is greater than the energy of the reactants. The total energy is absorbed in the form of heat and  for the reaction comes out to be positive.

Exothermic reactions are defined as the reactions in which energy of the product is lesser than the energy of the reactants. The total energy is released in the form of heat and  for the reaction comes out to be negative.

Thus H_2(g)+F_2(g)\rightarrow 2HF(g) evolves heat , it is exothermic in nature. The value of q is -542kJ.

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1. 51.2 g of NaClO (pKa of HClO is 7.50) and 25.3 g of KF (pKa of of HF is 3.17) were combined in enough water to make 0.250 L o
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Answer:

* pH=11.0

* [HClO]_{eq}=9.32x10^{-4}M

* [HF]_{eq}=5.07x10^{-6}M

Explanation:

Hello,

At first, the molarities of NaClO and KF are computed as shown below:

M_{NaClO}=\frac{51.2g*\frac{1mol}{74.45g} }{0.250L}=2.75M \\\\M_{KF}=\frac{25.3g*\frac{1mol}{58.1g} }{0.250L} =1.74M

Now, since both NaClO and KF are ionic, one proposes the dissociation reactions as:

NaClO\rightarrow Na^++ClO^-\\KF\rightarrow K^++F^-

In such a way, by writing the formation of HClO and HF respectively, due to the action of water, we obtain:

ClO^-+H_2O\rightleftharpoons HClO+OH^-\\F^-+H_2O\rightleftharpoons HF+OH^-\\

Now, the presence of OH⁻ immediately implies that Kb for both NaClO and KF must be known as follows:

Kb=\frac{Kw}{Ka} \\Kb_{NaClO}=\frac{1x10^{-14}}{10^{-7.50}}=3.16x10^{-7}\\Kb_{KF}=\frac{1x10^{-14}}{10^{-3.17}}=1.48x10^{-11}

In such a way, the law of mass action for each case is:

Kb_{NaClO}=3.16x10^{-7}=\frac{[HClO][OH]^-}{[ClO^-]}=\frac{(x_{ClO})(x_{ClO})}{2.75-x_{ClO}}\\Kb_{KF}=1.48x10^{-11}=\frac{[HF][OH]^-}{[F^-]}=\frac{(x_{F})(x_{F})}{1.74-x_{F}}

Now, by solving for the change x for both the ClO⁻ and F⁻ equilibriums, we obtain:

x_{ClO}=9.32x10^{-4}M\\x_{F}=5.07x10^{-6}M

Such results equal the concentrations of OH⁻ in each equilibrium, thus, the total concentration of OH⁻ result:

[OH^-]_{tot}=9.32x10^{-4}M+5.07x10^{-6}M=9.37x10^{-4}M

With which the pOH is:

pOH=-log(9.37x10^{-4})=3.03

And the pH:

pH=14-pOH=11.0

In addition, the equilibrium concentrations of HClO and HF equals the change x for each equilibrium as:

[HClO]_{eq}=x_{ClO}=9.32x10^{-4}M

[HF]_{eq}=x_{F}=5.07x10^{-6}M

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