Question

1. To interpret and compare heats of reaction (Hrxn), standard states must be used. What are the standard states for a gas, an aqueous solution, and a pure substance? Why are they important?
2. Under what circumstances is the enthalpy of formation of a compound from its elements usually:

a. positive?
b. negative?

Explain each answer.
3. Calculate the heat of reaction (ΔHrxn) for the following reactions, using heats of formation (ΔHf). Show your work. Refer to a table of heats of formation in your textbook as needed.

5O2(g) + 4NH3(g) → 6H2O(g) + 4NO(g)

Answer 1

@Hoslos

Answer 2

For a gas its (g), for an aqueous solution (aq) and pure substance, which I think its a solid its (s). They are importabt, because when we are given reactions, the states are important to make sure whether or not the reaction is possible. Also we can be able to determine the states of the products of the reaction.

Answer 3

2. Enthalpy change of formation is positive when the reactants end up absorbing energy and are negative when energy is released.

Answer 4

ok so now a) and b) ?

Answer 5

Are both in 2.

Answer 6

OK thanks now just #3 :)

Answer 7

The energy of elements in their standard states is 0, meaning this applies to oxygen
E= - energy of reactants + energy of products
E = - (12*390) + [12(460) + (4*143)] = ?

Answer 8

10772?

Answer 9

-4680 + 6092= 1412Kj/mol.

Answer 10

ok thanks! :)

Answer 11

Any time.