Question

consider the reaction
ccl₄ + o₂ → co₂ + cl₂
when balanced using the smallest possible
integer coefficients, what will be the sum of the
coefficients?
1 8
2 7
3 6
4 5
5 10
6 12
7 4
8 9
9 11

Explanation:

Step1: Balance Carbon

The number of C atoms on the left (in $\ce{CCl4}$) is 1, so on the right (in $\ce{CO2}$) it should also be 1. So coefficient of $\ce{CO2}$ is 1, and $\ce{CCl4}$ remains 1 for now. Reaction: $\ce{CCl4 + O2 -> CO2 + Cl2}$ (C balanced).

Step2: Balance Chlorine

Left: 4 Cl (in $\ce{CCl4}$), so right (in $\ce{Cl2}$) needs 4 Cl. Since $\ce{Cl2}$ has 2 Cl per molecule, coefficient of $\ce{Cl2}$ is $\frac{4}{2}=2$. Now reaction: $\ce{CCl4 + O2 -> CO2 + 2Cl2}$ (Cl balanced).

Step3: Balance Oxygen

Left: $\ce{O2}$ (let coefficient be $x$), right: $\ce{CO2}$ has 2 O. So $2x = 2$ (from $\ce{CO2}$), so $x = 1$? Wait, no: Wait, $\ce{CCl4 + O2 -> CO2 + 2Cl2}$. Left O: $2x$, right O: 2 (from $\ce{CO2}$). So $2x = 2$ → $x = 1$? Wait, but let's check again. Wait, the original reaction: $\ce{CCl4 + O2 -> CO2 + Cl2}$. After balancing C (1) and Cl (2), we have $\ce{CCl4 + O2 -> CO2 + 2Cl2}$. Now O: left is $2$ (from $\ce{O2}$), right is $2$ (from $\ce{CO2}$). Wait, that's balanced? Wait, no: Wait, $\ce{CCl4}$ has no O, $\ce{O2}$ has O, $\ce{CO2}$ has O. So left O: $2$ (from $\ce{O2}$), right O: $2$ (from $\ce{CO2}$). So the balanced equation is $\ce{CCl4 + O2 -> CO2 + 2Cl2}$? Wait, no, wait: Wait, let's count O again. Wait, $\ce{CO2}$ has 2 O, so right O is 2. Left O is from $\ce{O2}$, so coefficient of $\ce{O2}$ is 1. So the balanced equation is $\ce{CCl4 + O2 -> CO2 + 2Cl2}$? Wait, but let's check all atoms:

• C: 1 (left) vs 1 (right) – good.
• Cl: 4 (left) vs 2×2=4 (right) – good.
• O: 2 (left, from $\ce{O2}$) vs 2 (right, from $\ce{CO2}$) – good. Wait, so the balanced equation is $\ce{CCl4 + O2 -> CO2 + 2Cl2}$? Wait, but that seems too easy. Wait, maybe I made a mistake. Wait, no, let's check again. Wait, the reaction is $\ce{CCl4 + O2 -> CO2 + Cl2}$. Let's list coefficients:

$\ce{CCl4}$: 1, $\ce{O2}$: 1, $\ce{CO2}$: 1, $\ce{Cl2}$: 2. Now sum of coefficients: 1 (CCl4) + 1 (O2) + 1 (CO2) + 2 (Cl2) = 1+1+1+2=5? Wait, but the options have 5 as option 4 (4 5). Wait, but let's confirm. Wait, maybe I messed up. Wait, another way: Let's write the equation again.

Wait, maybe the correct balancing is: Wait, $\ce{CCl4 + O2 -> CO2 + Cl2}$. Let's use oxidation states? No, simple balancing.

C: 1 on left, 1 on right – good.

Cl: 4 on left, 2 on right (if $\ce{Cl2}$ is 1) – no, so $\ce{Cl2}$ must be 2 (4 Cl).

O: 2 on left (O2), 2 on right (CO2) – so O2 is 1.

So coefficients: $\ce{CCl4}$:1, $\ce{O2}$:1, $\ce{CO2}$:1, $\ce{Cl2}$:2. Sum: 1+1+1+2=5. So the sum is 5.

Answer:

4 5