Question

1.Use the bond dissociation energies found on page 219 of your textbook to calculate the ΔHº in kilojoules for 2NH3(g) + Cl2(g) à N2H4(g) + 2HCl (g)

2.Define standard heat of formation? Are the following exothermic or endothermic, an increase or decrease in entropy? Solid turning to gas, gas turning to liquid, liquid turning to solid.

3.If it takes 20 Joules of energy to change 5 grams of a substance from 20 C to 25 C, what is the specific heat?

Answer 1

3. As we know that heat energy is given by equation

Heat energy = mass x T x S

Where T is the temperature difference and S is the specific heat.

S = 20J/5g x (25-20)C =20/25 = 0.8 J/g⁰C

2. The standard heat of formation of a compound is defined as the change of enthalpy during the formation of one mole of the substance from its constituent particles, with all substances in their standard states at 1bar pressure.

Since The textbook page no. 219 is missing so it's difficult to find the answer to question 1 and without H value we can't tell about the nature of the reaction whether it is exothermic or endothermic. But generally, if H is negative than the reaction will be exothermic of if it's positive than reaction will be endothermic.