A3 - Formation and Combustion Enthalpy Flashcards
Define standard enthalpy of formation
The enthalpy change when one mole of a substance is formed from its elements under standard conditions
What is there always one mole of in an enthalpy of formation equation?
There is one mole of the substance being formed
What must a substance be formed from in an enthalpy of formation equation?
Its elements in their standard states
What substances have an enthalpy of formation of zero?
Elements in their standard states
What is the enthalpy of formation for an element in its standard state?
Zero
When would an element have an enthalpy of formation that is not zero?
When the element is not in its standard state
Which elements are diatomic?
H2, F2, Cl2, Br2, I2, O2, N2
What are standard conditions?
Temperature = 298 K. Pressure = 100 kPa
Define standard enthalpy of combustion
The enthalpy change when one mole of a substance is completely combusted under standard conditions
What type of combustion must happen when during an enthalpy of combustion?
Complete combustion
What are the products for an enthalpy of combustion?
CO2 and/or H2O
What substances have an enthalpy of combustion of zero?
CO2 and H2O
Why does CO have an enthalpy of combustion that is not zero?
Because CO is a product of incomplete combustion, so it can be combusted further
Why do CO2 and H2O have enthalpies of combustion of zero?
Because they are products of complete combustion and can’t be combusted
What is there always one mole of in an enthalpy of combustion equation?
There is one mole of the substance being combusted?
