How many moles of water (H2O) would be produced if 10 moles of O2 gas reacted completely with excess H2 gas?2 H2(g) + O2(g) → 2 H2O(g)A. 5 B. 10 C. 20 D. 30 

Answer:C. 20
Explanation:Use the equation to know that 1 mol of O2 is equal to 2 mol H2O.
Now you will start with the data, this is 10 mol O2 and you obtain:

10 mol O2  x 2 mol H2O    =  20 mol H2O                         1 mol O2

2 H2(g) + O2(g) → 2 H2O(g)according to the reaction:1 mole of O2-----------------2 moles of H2O10 moles of O2--------------------- xx = 20 mole of H2Oanswer: C