25. Hydrazine, N,H, is a liquid used as a rocket fuel. It reacts with oxygen to

Question

25. Hydrazine, N,H, is a liquid used as a rocket fuel. It reacts with oxygen to yield nitrogen gas and water. The reaction of 650 g N,H, evolves 1262 kJ of heat.Calculate the enthalpy change per mole of hydrazine combusted. a. -19.4kJ/mol b.-25.6 kJ/mol c.-126 k/mol d.-622 kJ/mol e.-820. kJ/mol 26. Which of the following statements is/are CORRECT? FM radio waves have longer wavelengths than visible radiation and AM radio waves have shorter wavelengths than visible radiation 2. Magnetic resonance imaging (MRI) uses a mixture of x-rays and gamma rays 3. Exposure to ultraviolet (UV) radiation can lead to sunburns. b. 2only c.3 only d.1 and 2 e. 1, 2, and 3 a. I only 27. A hot piece of iron is dropped into a beaker containing colder water. Which of the following statements is/are CORRECT? Encrgy is transferred as heat from the iron to the water Thermal equilibrium is atained when the iron and the water reach the same temperature. Thermal energy from the iron is conven.ed to electrostatic energy in the water 1. 2. 3. a. I only b. 2 omly .3 only d. 1 and 2 e. 1,2, and 3 -2043.0 kJ 28. The standard enthalpy change for the combustion of I mole of propane is GI1g(g) + 5 O2(g) 3 CO2(g) + 4 H20(g) Calculate Ar for propane based on the following standard molar enthalpies of formation. AI (kJ/mol-rxn) molecule COg) H20(8) a.-1407.7 k/mol-rxn b. +104.7 kimol-rxn c.-104.7 kJ/mol-rxn d.-4190.7 kJ/mol-rxn e. +1407.7 k/mol-rxn -241.8 functions: heat (q) work (w nthalpy change (An 29. Which of the following thermodynamic quantities are state and/or internal energy change (AU)? a, q only b.wonly c.&Monly; d.Uonly e.&Hand; U

Explanation / Answer

25.

We have reaction

N2H4 + O2 = N2 + 2 H2O

molar mass of N2H4 = 14 x 2 + 1x4 = 32g/mol

6.50g N2H4 evolves -126.2 kJ

1g -126.2 kJ /6.5

32g or 1 mol -126.2 kJ/6.5 x 32 = -621.29 kJ

heat evolved per mole = -621.29 kJ/mol ~ -622 kJ/mol

heat evolved is always negative

26.

only (c) is correct

all radio waves have longer wavelenth than visible

MRI uses powerful magnets,which uses protons of water in our body to create an image

27.

only 1 and 2 correct (d)

28.

Hrxn = Hfp - Hfr

Hfp and Hfr = enthalpy of formation of product and reactant respectively

-2043 kJ = 4 mol x -241.8 kJ/mol + (-393.5 kJ/mol) x 3 - (HfC3H8 - 0)

enthalpy of formation of oxygen molecule = 0

HfC3H8 = +104.7 kJ/mol

29.

ans (e)

  

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