Question

Galena is the ore from which elemental lead is extracted. in the first step of the extraction process, galena is heated in air to form lead(ii) oxide. 2pbs(s) + 3o2(g)  2pbo(s) + 2so2(g) h = –827.4 kj what mass of galena is converted to lead oxide if 975 kj of heat are liberated

Answer 1

When 975 kJ of heat are liberated in the process of converting galena (PbS) to lead oxide (PbO), a mass of 563.8 grams of galena is converted based on the reaction stoichiometry.

Step-by-step explanation:

The student is asking about the extraction process of lead from galena (PbS) where heat is liberated. To calculate the mass of galena converted to lead oxide (PbO) when 975 kJ of heat are released, we will use stoichiometry based on the given thermochemical equation:

2 PbS (s) + 3 O2 (g) → 2 PbO (s) + 2 SO2 (g) ΔH = −827.4 kJ

This shows that for every 827.4 kJ of heat released, 2 moles of PbS are converted to PbO. Using the molar mass of PbS (239.26 g/mol), the conversion from kJ to mass can be performed as follows:

2. First, find out how many kJ corresponds to one mole of PbS: 827.4 kJ for 2 moles, so 827.4 kJ / 2 = 413.7 kJ/mole.
4. Next, calculate the number of moles of PbS corresponding to 975 kJ: 975 kJ / 413.7 kJ/mole = 2.356 moles.
6. Finally, convert moles of PbS to mass: 2.356 moles * 239.26 g/mole = 563.8 grams.

Therefore, 563.8 grams of galena are converted to lead oxide with the liberation of 975 kJ of heat.

Answer 2

To illustrate clearly, I will rewrite the reaction in a more understandable manner.

2PbS (s) + 3 O₂(g) ⇒ 2 PbO(s) + 2 SO₂ (g) Δh = –827.4 kJ

Galena is PbS and Lead Oxide is PbO. This reaction has a negative sign for the change in enthalpy of reaction. The sign convention only means that the reaction releases energy to the surroundings. In other words, the reaction is exothermic. Focusing on only its magnitude, this means that 827.4 kJ of energy is needed for this reaction of 2 moles of Galena and 3 mole of O₂ to occur.

Now, if you had an energy of 975 kJ, then the reaction would proceed into completion and would even exceed in the number of moles of products produced. We use stoichiometric calculations as follows:

975 kJ * (2 mol PbS/827.4 kJ) = 2.357 moles of PbS

Knowing that the molar mass of Galena is 239.3 g/mol, then the mass of galena needed to produce PbO is

2.357 mol PbS *239.3 g/mol = 564 g galena