Question

1. identify which of the following is a complete and balanced chemical equation: a. h₂o → h₂ + o₂ b. nacl + h₂o c. fe + s → fes d. caco₃ 2. determine balanced chemical equations for the following chemical reactions: a. koh + hcl → kcl + h₂o b. nahco₃ → h₂o + co₂ + na₂co₃ c. pb(no₃)₂ + ki → kno₃ + pbi₂ 3. explain why balancing an equation requires changing the coefficients in front of chemical formulas rather than the subscripts within chemical formulas. 4. describe the information needed to calculate the mass of a reactant or product for the following balanced equation: fes + 2hcl → h₂s + fecl₂ 5. applying concepts chlorine gas is produced by the electrolysis of sodium chloride in water in the following reaction: 2nacl + 2h₂o → cl₂ + h₂ + 2naoh what mass of sodium chloride is needed to make 71 g of chlorine gas?

Explanation:

Step1: Identify balanced equation in question 1

A balanced chemical equation has equal numbers of each type of atom on both sides. For a. $H_2O
ightarrow H_2 + O_2$, there are 2 oxygen atoms on the right - hand side and 1 on the left - hand side, so it's unbalanced. For b. $NaCl + H_2O$, it's not a complete reaction equation. For c. $Fe+S
ightarrow FeS$, there is 1 Fe and 1 S on both sides, so it's balanced. For d. $CaCO_3$ is just a compound, not a balanced equation.

Step2: Balance equations in question 2

a. $KOH + HCl
ightarrow KCl + H_2O$ is already balanced (1 K, 1 O, 2 H, 1 Cl on both sides).
b. $NaHCO_3
ightarrow H_2O + CO_2+Na_2CO_3$ is unbalanced. The balanced equation is $2NaHCO_3
ightarrow H_2O + CO_2+Na_2CO_3$.
c. $Pb(NO_3)_2 + 2KI
ightarrow 2KNO_3+PbI_2$ is balanced (1 Pb, 2 N, 6 O, 2 K, 2 I on both sides).

Step3: Explain coefficient - subscript concept in question 3

Changing subscripts would change the identity of the chemical substance. For example, $H_2O$ is water, but $H_2O_2$ is hydrogen peroxide. Coefficients are used to balance equations because they just change the number of molecules of a substance without changing its chemical identity.

Step4: Determine information for mass - calculation in question 4

We need the molar masses of the reactants and products and the mole - ratio from the balanced equation. The molar mass of $FeS$ is $M_{FeS}=55.85 + 32.07=87.92\ g/mol$, $HCl$ is $M_{HCl}=1.01+35.45 = 36.46\ g/mol$, $H_2S$ is $M_{H_2S}=2\times1.01 + 32.07=34.09\ g/mol$, $FeCl_2$ is $M_{FeCl_2}=55.85+2\times35.45 = 126.75\ g/mol$. The mole - ratio of $FeS:HCl:H_2S:FeCl_2 = 1:2:1:1$.

Step5: Calculate mass of NaCl in question 5

First, find the molar mass of $Cl_2$, $M_{Cl_2}=2\times35.45 = 70.90\ g/mol$. The number of moles of $Cl_2$, $n_{Cl_2}=\frac{m_{Cl_2}}{M_{Cl_2}}=\frac{71\ g}{70.90\ g/mol}\approx1\ mol$. From the balanced equation $2NaCl + 2H_2O
ightarrow Cl_2 + H_2+2NaOH$, the mole - ratio of $NaCl$ to $Cl_2$ is 2:1. So the number of moles of $NaCl$ needed, $n_{NaCl}=2n_{Cl_2}=2\ mol$. The molar mass of $NaCl$ is $M_{NaCl}=22.99 + 35.45=58.44\ g/mol$. Then the mass of $NaCl$, $m_{NaCl}=n_{NaCl}\times M_{NaCl}=2\ mol\times58.44\ g/mol = 116.88\ g$.

Answer:

1. c. $Fe + S

ightarrow FeS$

1. a. $KOH + HCl

ightarrow KCl + H_2O$ (already balanced), b. $2NaHCO_3
ightarrow H_2O + CO_2+Na_2CO_3$, c. $Pb(NO_3)_2 + 2KI
ightarrow 2KNO_3+PbI_2$

1. Changing subscripts changes substance identity; coefficients change number of molecules.
2. Molar masses and mole - ratio.
3. $116.88\ g$