Question

Consider the equations below. (1) Ca(s) + CO2(g) + 1 2 O2(g) → CaCO3(s) (2) 2Ca(s)+O2(g) → 2CaO(s) How should you manipulate these equations so that they produce the equation below when added? Check all that apply. CaO(s) + CO2(g) → CaCO3(s) reverse the direction of equation (2) multiply equation (1) by 3 multiply equation (2) by 1/2

Answer 1

Answer : The correct options are, reverse the direction of equation (2) and multiply equation (2) by 1/2.

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.

The main given balanced chemical reaction is,

$CaO(s)+CO_2(g)\rightarrow CaCO_3(s)$

Now we have to determine the main chemical reaction from the given two intermediate reactions.

(1) $Ca(s)+CO_2(g)+\frac{1}{2}O_2(g)\rightarrow CaCO_3(s)$

(2) $2Ca(s)+O_2(g)\rightarrow 2CaO(s)$

Now reverse the equation (2), multiply equation (2) by 1/2 and then add both the equations, we get the main chemical reaction.

(1) $Ca(s)+CO_2(g)+\frac{1}{2}O_2(g)\rightarrow CaCO_3(s)$

(2) $CaO(s)\rightarrow Ca(s)+\frac{1}{2}O_2(g)$

Now add both the equations, we get:

$CaO(s)+CO_2(g)\rightarrow CaCO_3(s)$

Hence, the steps used for the main reaction are, reverse the direction of equation (2) and multiply equation (2) by 1/2.