How many liters of water are needed to make a 4.00 M solution using 75.0

Chemistry

1 answer:

timurjin [86]3 years ago

7 0

Answer:

0.22L

Explanation:

Given parameters:

Concentration of solution = 4.00M

Mass of lithium Bromide = 75g

Unknown:

Volume of water = ?

Solution:

Concentration in terms of the molarity is the number of moles of solute in a solution.

Molarity = $\frac{number of moles }{volume of solution}$

let us find the number of moles first;

Number of moles = $\frac{mass}{molar mass}$

Molar mass of LiBr = 7 + 80 = 78g/mol

number of moles = $\frac{75}{78}$

number of moles = 0.96moles

Volume of water = $\frac{number of moles }{molarity}$ = 0.96/4 = 0.22L

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At a certain temperature, Kc = 0.0500 and ∆H = +39.0 kJ for the reaction below, 2 MgCl2(s) + O2(g) → 2MgO(s) + Cl2(g) Calculate

Minchanka [31]

Explanation:

Since, it is shown that the reaction has been reversed. Therefore, value of $K_{c}$ will become $\frac{1}{K_{c}}$ .

Hence, new $K_{c'} = \frac{1}{K_{c}}$

= $\frac{1}{0.0500}$

= 20

Also, the number of moles of each reactant has been halved. So, $K_{c''}$ for the reaction $MgO(s) + \frac{1}{2}Cl2(g) → MgCl_{2}(s) + \frac{1}{2} O2(g)$ will also get halved.

Therefore, $K_{c''}$ = $K_{c'}$ = $(20)^{0.5}$

= 4.47

As the value of $\Delta H$ is given as +39.0 kJ. So, it means that the reaction is endothermic in nature. So, energy of reactants will be more than the products. Hence, according to Le Chatelier's principle reaction will move in the forward direction.