Question

Use the following information to calculate the amount of heat involved in the complete reaction of 6.309 of carbon to from PbCO3 (s) in reaction 4. Be sure to give the proper sign (positive or negative) with your answer. (1) pb(s)+1/2 O2 right arrow pbO(s) (2) c(g)+O2(g) right arrow CO2(g) (3) pbCO3(s)right arrow pbO(s)+CO2(g) (4) pb(s)+C(s)+3/2 O2(g) right arrow pbO3(s) delta H degree rsn= -219 kJ delta H degree rsn= -394 kJ delta H degree rsn= 86 kJ

Answer 1

Answer : The amount of heat involved in the complete reaction is -367.5 kJ

Explanation :

According to Hess’s law of constant heat summation, the heat absorbed or evolved in a given chemical equation is the same whether the process occurs in one step or several steps.

According to this law, the chemical equation can be treated as ordinary algebraic expression and can be added or subtracted to yield the required equation. That means the enthalpy change of the overall reaction is the sum of the enthalpy changes of the intermediate reactions.

The given main reaction is,

$Pb(s)+C(s)+\frac{3}{2}O_2\rightarrow PbCO_3(s)$    $\Delta H=?$

The intermediate balanced chemical reaction will be,

(1) $Pb(s)+\frac{1}{2}O_2(g)\rightarrow PbO(s)$     $\Delta H_1=-219kJ$

(2) $C(g)+O_2(g)\rightarrow CO_2(g)$    $\Delta H_2=-394kJ$

(3) $PbCO_3(s)\rightarrow PbO(s)+CO_2(g)$    $\Delta H_3=86kJ$

Now we will reverse the reaction 3 and then adding all the equations, we get :

(1) $Pb(s)+\frac{1}{2}O_2(g)\rightarrow PbO(s)$     $\Delta H_1=-219kJ$

(2) $C(g)+O_2(g)\rightarrow CO_2(g)$    $\Delta H_2=-394kJ$

(3) $PbO(s)+CO_2(g)\rightarrow PbCO_3(s)$    $\Delta H_3=-86kJ$

The expression for enthalpy of change will be,

$\Delta H=\Delta H_1+\Delta H_2+\Delta H_3$

$\Delta H=(-219kJ)+(-394kJ)+(-86kJ)$

$\Delta H=-699kJ$

Now we have to calculate the moles of carbon.

$\text{Moles of carbon}=\frac{\text{Mass of carbon}}{\text{Molar mass of carbon}}$

Molar mass of carbon = 12 g/mole

$\text{Moles of carbon}=\frac{6.309g}{12g/mole}=0.5258mole$

Now we have to calculate the amount of heat involved in the complete reaction.

As, 1 mole of carbon involved heat = -699 kJ

So, 0.5258 moles carbon involved heat = 0.5258 × (-699 kJ) = -367.5 kJ

Therefore, the amount of heat involved in the complete reaction is -367.5 kJ