A gas is held at 120.4 kPa and 333K. When the temperature is decreased to
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Answer:
<h3>(a)</h3> per mole reaction.
per mole reaction.
Explanation:
What is the standard enthalpy of formation of a substance?
the enthalpy change when one mole of the substance is formed from the most stable allotrope of its elements under standard conditions.
Naturally, for the most stable allotrope of each element under standard conditions. For example, oxygen
(not ozone
) is the most stable allotrope of oxygen. Also, under STP
is a gas. Forming
from itself does not involve any chemical or physical change. As a result,
for
.
Look up standard enthalpy of formation data for the rest of the species. In case one or more values are not available from your school, here are the published ones. Note the state symbols of the compounds (water/steam
in particular) and the sign of the enthalpy changes.
:
;
:
;
:
;
:
;
:
;
:
How to calculate the enthalpy change of a reaction (or simply
from enthalpies of formation?
- Multiply the enthalpy of formation of each product by its coefficient in the equation.
- Find the sum of these values. Label the sum
to show that this value takes the coefficients into account.
- Multiply the enthalpy of formation of each reactant by its coefficient in the equation.
- Find the sum of these values. Label the sum
to show that this value takes the coefficient into account.
- Change = Final - Initial. So is the case with enthalpy changes.
.
For the first reaction:
;
;
.
Try these steps for the second reaction:
.