An exothermic reaction is a reaction that releases energy.
-<u><em>Oxygen</em></u>
According to Google these are the percentages of the <em>Earths Atmosphere</em>
<em>1</em> 78% - Nitrogen
<u>2</u> 21% - Oxygen
<em>3</em> 0.9% - Argon
<em>4 </em>0.3 - Carbon Dioxide with very small percentage of other elements.
Ok percent error is abs(calculated-actual)/actual(100%)
So 1.5/96 *100%
Yes, an OH group from ethanol can form a hydrogen bond to the ether O atom in the same way as it can do so with the single-bonded O atom in the ester.
The O atom in the carbonyl group of the ester can also form H-bonds with ethanol.