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Natalka [10]
3 years ago
7

Using the equations and enthalpy values provided, which mathematical expression can be used to determine the unknown enthalpy ch

ange represented by x?
3C + 3O2 yields 3CO2 deltaH = -1182 kJ

4H2 + 2O2 yields 4H2O deltaH =-1144 kJ

C3H8 + 5O2 yields 3CO2 + 4H2O deltaH = x

3H8 3C + 4H2 H = 104 kJ

A. 104 = (-1182) - [x + (-1144)]

B.104 = x - [(-1182) + (-1144)]

C.104 = (-1182) + (-1144) + x

D.104 = x + (-1182) - (-1144)
Chemistry
2 answers:
natita [175]3 years ago
5 0

Answer:

B. 104 = x - [(-1182) + (-1144)]

Explanation:

The unknown entahlpy change for the given equation is determined by the Hess's Law.

3C + 3O2 → 3CO2  ΔH = -1182 kJ      ....(a)

4H2 + 2O2  → 4H2O  ΔH =-1144 kJ   ....(b)

C3H8 → 3C + 4H2  ΔH  = 104 kJ  ....(c)

C3H8 + 5O2  →  3CO2 + 4H2O   ΔH = x   ....(d)

The unknown enthalpy change x is calculated as follows,

The equation (d) is obtained by the adding equation (a), equation (b ) and equation (c) .Therefore, the value of the unknown enthalpy change x will be equal to the sum of all enthalpy change value of the respective equation.

104 = x - [(-1182) + (-1144)]

vlabodo [156]3 years ago
3 0
In order to solve this, we need to make use of Hess' Law.

We are already given the equations and their corresponding deltaH. Using Hess' Law, we can generate this equation:
104 kJ = x - (-1182 kJ) - (-1144 kJ)

Among the choices, the answer is
<span>B.104 = x - [(-1182) + (-1144)] 
</span>
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In their notebook you see that it takes 9 hours for a sixth of a 0.5M solution of BC2 to react. Unfortunately, you have somewher
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Complete Question

The complete question is shown on the first uploaded image

Answer:

The concentration of BC_2 that should used originally is C_Z_o = 0.4492M

Explanation:

     From the question we are told that

         The necessary elementary step is  

                  2BC_2 ----->4C + B_2

          The  time taken for sixth of 0.5 M of reactant to react t = 9 hr

           The time available is t_a = 3.5 hr

             The desired concentration to  remain C  = 0.42M

Let Z be the reactant ,   Y be the first product and X the second product

Generally the elementary rate  law is mathematically as

                    -r_Z = kC_Z^2 = - \frac{d C_Z}{dt}

Where k is the rate constant ,  C_Z is the concentration of Z

From the elementary rate law we see that the reaction is second order (This because the concentration of the reactant is raised to power 2 )

 For second  order reaction

            \frac{1}{C_Z}  - \frac{1}{C_Z_o}  = kt

Where C_Z_o is the initial concentration of Z which a value of   C_Z_o = 0.5M

       From the question we are told that it take  9 hours  for the concentration of  the reactant to become

                 C_Z =  C_Z_o - \frac{1}{6}  C_Z_o

                  C_Z = 0.5  - \frac{0.5}{6}

                       = 0.4167 M

So      

                     \frac{1}{0.4167}  - \frac{1}{0.50}  =  9 k

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                =>    k = 0.044\  L/ mol \cdot hr^{-1}

  For   C_Z = 0.42M

                \frac{1}{0.42} - \frac{1}{C_Z_o}  = 3.5 * 0.044

                2.38 -  0.154  =    \frac{1}{C_Z_o}

                           2.226  =    \frac{1}{C_Z_o}

                            C_Z_o = \frac{1}{2.226}

                             C_Z_o = 0.4492M

                       

           

             

         

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