Scientific Understanding

**Example**: What is the Δ n (delta n) of the equation below?

N_{2(g)} + 3 H_{2(g)} <—-> 2 NH_{3(g)}

Answer: Δ n = 2 – 4 = -2

**VIDEO Calculating the DELTA N (** **Δn )**** Demonstrated Example 1**: What is the Δn (delta n) of the equation below?

H_{2}SO_{4(aq)} <—–> H_{2(aq)} + S_{(s)} + 2 O_{2(aq)}

Add together all of the coefficients of the products that involve (aq) or (g) phases.

Answer: 1 H_{2} + 2 O_{2} = 3. (S is not counted because it is solid phase)

Add together all of the coefficients of the reactants that involve aq or g phases.

Answer: 1 H_{2}SO_{4} = 1

Take the sum of the products minus the sum of the reactants.

Answer: 3 – 1 = 2

COMPLETE ANSWER: Δn = 2

**VIDEO Calculating the DELTA N (** **Δn )**** Demonstrated Example 2**: What is the Δn (delta n) of the equation below? GIVE A NEGATIVE ANSWER

**PRACTICE PROBLEMS**: solve for the Δ n (delta n) in each problem.

What is the Δ n of the equation below?

MgBr_{2(aq)} + 2 NaI_{(aq)} <——> MgI_{2(aq)} + 2 NaBr_{(aq)}

Answer: 3 – 3 = Zero

What is the Δ n of the equation below?

2 H_{2}O_{(g)} <—-> 2 H_{2(g)} + O_{2(g)}

Answer: 3 – 2 = 1

What is the Δ n of the equation below?

2 Fe^{3+}_{(aq)} + 3 CO_{3}^{2-}_{(aq)} <—-> Fe_{2}(CO_{3})_{3(s)}

Answer: 0 – 5 = -5 don’t count Fe_{2}(CO_{3})_{3}

What is the Δ n of the equation below?

C_{4(s)} + 4 O_{2(g)} <—-> 4 CO_{2(g)}

Answer: 4 – 4 = Zero don’t count C_{4}