Answered By Leonardo F

It's all about molar mass and reactions. We know that the reaction is:

 $Zn\left(s\right)+O\left(g\right)->ZnO\left(s\right)$Zn(s)+O(g)−>ZnO(s) 

Hence, we know that the molar proportion from Zn(s) to ZnO(s) is 1:1. That is, 1 mol of Zn(s) reacts with 1 mol of O(g) to produce 1 mol of ZnO(s). Since the enthalpy change for the reaction is 350.5 kJ, this means that for every mol of Zn(s) consumed, the energy released is 350.5 kJ. Since the molar proportion is 1:1, we know that for every mol of ZnO(s) the energy released is also 350.5 kJ. The molar mass of ZnO(s) is:

65.38+16=81.38 g/mol.

So, we know that:

  $81.38g->350.5kJ$81.38g−>350.5kJ  

 $25g->x$25g−>x 

Solving the rule of three, we know that the energy released to form 25 g of ZnO(s) is:

 $25\times350.5\div81.38=107kJ$25×350.5÷81.38=107kJ 

Respecting the amount of significant digits, the energy released is approximately 107 kJ.

Answered By Leonardo F

Actually, the reaction wrote in the question is not accurate. The correct reaction is:

 $Zn\left(s\right)+O2\left(g\right)->2ZnO\left(s\right)$Zn(s)+O2(g)−>2ZnO(s) 

Answered By Leonardo F

Given the corerct reaction above, the mass needs to be changed:

 $162.76g->350.5kJ$162.76g−>350.5kJ 

 $25g->x$25g−>x 

 $x=25\times350.5\div162.76=53.8kJ$x=25×350.5÷162.76=53.8kJ