What is the standard change in enthalpy of formation of #"MgO"(s)#?

The reaction is:

#"Mg"(s) + 1/2 "O"_2(g) -> "MgO"(s)#

Answer 1

The standard enthalpy change of formation, or #DeltaH_f^@#, of magnesium oxide will be -601.6 kJ/mol.

The reaction you're using represents the formation of magnesium oxide from its elements in their most stable forms at standard state, #25^@"C"# and #"1 atm"#.

In the case of formation reactions, the standard enthalpy change of formation for a compound is measured, not calculated; usually, you'll find this value listed either in books or online.

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So, in your case, the standard enthalpy change of formation for magnesium oxide was measured to be

#DeltaH_f^@ = "-601.6 kJ/mol"#.

In every day language, the large negative value indicates that this process releases quite a bit of energy as can be observed in the video below.

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Answer 2

Henry Antrim

The standard change in enthalpy of formation of MgO(s) is approximately -601.8 kJ/mol.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

What is the standard change in enthalpy of formation of #"MgO"(s)#?

The reaction is: #"Mg"(s) + 1/2 "O"_2(g) -> "MgO"(s)#

The reaction is:

#"Mg"(s) + 1/2 "O"_2(g) -> "MgO"(s)#