Enthalpy of Formation

N2H4(g) + H2(g)--> 2 NH3(g) H1 = –1876kJ

3 H2(g) + N2(g)--> 2 NH3(g) H2 = –922 kJ

The H.f for the formation of hydrazine: 2 H2(g) + N2(g)--> N2H4(g) will be______kj/mol

I am very confused here. I thought I would just add H1 and H2 and divide by the molar mass of N2H4, but that is not correct. Please Help. Thank You!

  1. 👍
  2. 👎
  3. 👁
  1. I got the answer to be 95.4 kj/mol
    I reversed the 1st equation to get an overall 187.6 kj = h1
    then I just added that to H2 and I got the answer.
    But I still don't really understand the processes. If someone could explain that to me I would truly appreciate it.

    1. 👍
    2. 👎
  2. You have to reverse the direction of one reaction and change the sign of H.

    3 H2+ N2--> 2 NH3 H2 = -922 kJ/mole
    2NH3 -> N2H4 + H2 H = +1876 kJ/mole

    NOW add, and cancel out terms that appear on both sides.

    N2 + 2H2 -> N2H4 H = -954 kJ

    There is another problem. Your heat of formation of NH3 does not agree with accepted data. It should be -10.97 kJ/per mole of NH3, or twice that much for the reaction as written (which forms two moles). Also, the standard form of N2H4 at room temperature is a liquid, and your reaction involves the gas.

    1. 👍
    2. 👎
  3. For what it is worth, the correct heat of formation of N2H4 (liq.) is +12.10 kcal/mole and for N2H4(g) it is +22.79 kcal/mole. Those values are at 298 K. They are a few kcal/mole different at 0 K. Multiply by 4.18 for kJ/mole. That gives +95.3 kJ/mole for the N2H4(g) heat of formation, which agrees well with your second answer. You seem to have misplaced decimal points in your first version of the question.

    Those values come from the JANAF Thermochemcial Tables of the U.S National Bureau of Standards, 2nd edition.

    1. 👍
    2. 👎

Respond to this Question

First Name

Your Response

Similar Questions

  1. Honors Chemistry

    "How many grams of NH3 can be produced from the reaction of 28 g of N2 and 25 g of H2? N2 + 3H2 ---> 2NH3 ==> 28 g N2 x (1 mol N2/14.0 g N2) x (2 mol NH3/1 mol N2) x ( 17.0 g NH3/ 1 mol NH3) = 68 g NH3 25 g H2 x ( 1mol H2/2.0 g

  2. Chemistry

    Calculate the molarity and the molality of an NH3 solution made up of 30 g of NH3 in 70 g of water. The density of the solution is 0.982 g/ml. Molar Mass of NH3 = 17.04 g

  3. chemistry

    Nitrogen (N2) and hydrogen (H2) react to form ammonia (NH3). Consider a mixture of six nitrogen molecules and six hydrogen molecules in a closed container. Assuming the reaction goes to completion, what will the final product

  4. Chemistry

    If 2.50 g of CuSO4 are dissolved in 9.4 102 mL of 0.34 M NH3, what are the concentrations of Cu(NH3)42+, NH3 and Cu2+ at equilibrium? i tried doing Cu2+ first and i did Kf=5e13= salt/cu2+ nh3+^4 and i did molesCuSO4/.94 L = .01666

  1. chemistry

    How many moles are in 1.50 x 1023 molecules NH3? A. 2.49 x 10 -1 mol NH3 B. 2.49 x 101 mol NH3 C. 2.65 x 10 -1 mol NH3 D. 2.78 x 10 1 mol NH3 maybe B

  2. Chem help

    Which reaction of ammonia does not involve the non-bonding pair of electrons on the nitrogen atom? A NH3(g) + CH3I(g) → CH3NH 3+ I –(s) B NH3(g) + HCl (g) → NH4Cl (s) C 2NH3(l) + 2Na(s) → 2NaNH2(s) + H2(g) D 2NH3(aq) +

  3. Chemistry

    Consider this equilibrium N2(g) + H2(g) NH3(g) +94 kJ The equilibrium law exoression for the balanced chemical equationwould be A. [N2][H2]/[NH3] B. [NH3]/[H2][N2] C. [NH3]2/[H2][N2] D. [NH3]2/[H2]3[N2] E. 2[NH3]2/3[H2]3[N2]

  4. science

    Calculate the solubility of silver chloride in 10.0 M ammonia given the following information: Ksp (AgCl) = 1.6 x 10^–10 Ag+ + NH3--->AgNH3+ K=2.1x10^3 AgNH3+ + NH3-----> Ag(NH3)2+ K=8.2x10^3 Answer : 0.48 M Calculate the

  1. Chemistry

    How many moles are in 1.50 x 1023 molecules NH3? A. 2.49 x 10 -1 mol NH3 B. 2.49 x 101 mol NH3 C. 2.65 x 10 -1 mol NH3 D. 2.78 x 10 1 mol NH3

  2. AP Chem

    At a certain temperature, 4.0 mol NH3 is introduced into a 2.0 L container, and the NH3 partially dissociates by the reaction. 2 NH3(g) N2(g) + 3 H2(g) At equilibrium, 2.0 mol NH3 remains. What is the value of K for this reaction?

  3. chemistry

    from the balanced equation 4NH3 +7O2 - 4NO2 + 6H2O How many molecules of water are produced when 2.25 moles of ammonia are completely reacted? The equation tells us that 4 mol NH3 will produce 6 mols water. That means 2 mols NH3

  4. Chemistry

    Calculate the molar concentration of uncomplexed Zn2+ (aq) in a solution that contains 0.22 mol of Zn(NH3)4 2+ per liter and 0.3109 M NH3 at equilibrium. Kf for Zn(NH3)4 2+ is 2.9 X 10^9 I started this way... (0.3109 +

You can view more similar questions or ask a new question.