If we reverse the reaction to read z + w -> x + y, the +deltah would be a -delta h. does this indicate that heat is given off or absorbed in the reverse reaction

In this reaction heat is released

Explanation:

Exothemic Reactions : Those reactions in which heat is released when the products are  formed .

For such reaction The enthalpy change is negative.

for exothermic reaction

Endothermic Reactions : Those reaction which proceed by absorbing heat . Here heat is absorbed. The enthalpy change for such reactions is positive.

When the direction of reaction reverses , the value of H also changes.

In the given reaction,

 = heat is absorbed

So,

= heat is released

Exothermic reactions are more spontaneous as compared to endothermic ractions. This means that they  proceed own their own . Only little amount of energy is supplied to exothermic reaction to produce the prodct.

there all right good

explanation:

c (diamond),

sio2 (quartz)