Favorable (exergonic) chemical reactions:

a) are generally explosive
b) absorb energy from the surroundings
c) occur only in the gaseous phase
d) usually give off heat energy

Usually give off heat energy

Explanation:

Exergonic reactions are the ones which are spontaneous. Spontaneous reactions are indicated by the negative change in the Gibbs free energy. In order to provide characteristics for an exergonic reaction, we need to define the Gibbs free energy in terms of the enthalpy change and the entropy change:

Here:

is the enthalpy change;

is the entropy change;

is the absolute temperature.

In order to achieve a negative value in the Gibbs free energy change, we should have:

This is true for all temperatures if:

The major term here is the change in enthalpy, notice that we wish the enthalpy change to be negative.

Negative enthalpy change corresponds to an exothermic reaction, the one which releases heat. This means exergonic reactions would usually give off heat.

The mass of iron in the ore is 10.9 g

Explanation:

We are given:

Mass of iron (III) oxide = 15.6 g

We know that:

Molar mass of Iron (III) oxide = 159.69 g/mol

Molar mass of iron atom = 55.85 g/mol

As, all the iron in the ore is converted to iron (III) oxide. So, the mass of iron in iron (III) oxide will be equal to the mass of iron present in the ore.

To calculate the mass of iron in given mass of iron (III) oxide, we apply unitary method:

In 159.69 g of iron (III) oxide, mass of iron present is

So, in 15.6 g of iron (III) oxide, mass of iron present will be =

Hence, the mass of iron in the ore is 10.9 g