Chapter 9 - Enthalpy Changes Flashcards
What is enthalpy change?
The amount of heat or energy within a chemical system or the bonds of the substances presents.
What is a positive Change Energy
Endothermic
What is Hess’s Law
If a reaction can take place in 2 routes without changing the conditions, then both the routes have the same enthalpy change.
How to calculate the Change in Enthalpy (Delta H)
Total energy products - total energy reactants.
What is the energy change of a single element
0
How to calculate the Change in Enthalpy using the combustion values
Total energy reactants - Total energy products
What states do the elements have to be for the enthalpy values to count?
GASES!
Limitations of using Bond Enthalpy averages?
The actual values can vary depending on the chemical environment.
Also, there may be incomplete combustion, or the heat released to the surroundings.
Define the average Bond Enthalpy values
The energy required to break 1mol of a specific type of bond in a molecule in its gaseous phase.
What is a chemical system?
A collection of atoms, ions or molecules that participate in a chemical reaction
Endothermic Reaction- graph
Down to up.
Endothermic reaction explanations
Bond breaking absorbs energy and bond making releases energy. In an endothermic reaction, more energy is absorbed than released.
Exothermic reactions- graphs
Up then down.
Exothermic reactions - explanations
Bond breaking absorbs energy and bond making releases energy. In an exothermic reaction, more energy is released than absorbed.
Equation to fin the delta H r
Q/n (energy absorbed by the surroundings/ moles of chemical system)
