Unit 10 Flashcards
When bonds are made is energy input or output?
Output
When bonds are broken is energy input or output?
Input
What is an exothermic reaction?
When heat is given out. In the bonds in the products are stronger, they’re more energetically stable than the reactants
What is an endothermic reaction?
Energy is taken in. Bonds in the products are weaker and less energetically stable than the reactants
What is enthalpy change?
a heat change that takes place at constant pressure
What does standard enthalpy mean?
The heat change taking place at 1 ATM
What is a state function? and give examples
Depends on where you are not how you got there. Temp
Vol
Pressure
Is enthalpy a state function?
Yes it only depends on the beginning and the end
For an exothermic reaction what is enthalpy?
negative
For endothermic reaction what is enthalpy?
Positive
What is the transition state of a chemical reaction?
it is the intermediate configuration where potential energy is at its highest. It corresponds with activation energy
What is Hess’ law?
enthalpy of a chemical reaction is independent of the path. (reactions to get to final)
What is standard state?
It is how an element appears at 1 ATM and 25C
What is the enthalpy content of an element in its standard state?
0
What is standard heat of formation?
enthalpy change when one mole of substance is made from elements in their standard states
What is the standard heat of combustion?
enthalpy change when one mole of substance is completely burned with oxygen to form c02 and h20
What is heat of atomisation?
Enthalpy change when one mole of substance in its standard state is changed to atoms in gaseous state
What is solids turned directly into gases called?
Heats of sublimation
Heat of combustion hess law cycle
Reactants —–> products
↓ ↓
CO2 + H2O
If you want to go the other way to what an arrow if facing, just change the sign
heat of formation hess law cycle
Reactants ——> Products
↑ ↑
Elements standard state
If you want to go opposite of the arrow flip the sign
What is the unit of enthalpy?
KJ Mol -1
What will heat change be equal to?
Enthalpy change
