4P- Energetics Flashcards
What’s enthalpy change
Change in heat energy measured under conditions of constant pressure
What’s standard enthalpy change
Change in heat energy under standard conditions (100kPa and 298K)
When is enthalpy change -ve
Exothermic reactions or when temp rises or bond breaking
When is enthalpy change +ve
Endothermic reactions or when temperature decreases or bond making
What’s the definition of standard enthalpy of combustion
Enthalpy change when one mol of substance is completely burned in oxygen under constant pressure
All products in their standard states and standard conditions
What’s the definition of standard enthalpy of formation
Enthalpy change when one mol of substance formed from its constituent elements under standard conditions
Products in their standard states
Equation for heat energy
Q= mc^t
Q= heat change in joules
M= mass in g
T= change in temp in k or °c
Equation for enthalpy change
Enthalpy change= heat energy/mol
Heat energy needs to be in Kj
Equation for enthalpy change of formation of formation data is given
Sum of products - sum of reactants
Equation for enthalpy change of combustion if combustion data is given
Sum of reactants - sum of products
Equation for bond enthalpies if all compounds are in gaseous state (if not use the enthalpy of vaporisation value
Sum of bonds broken - sum of bonds made
Break (+ve enthalpy)- make (-ve enthalpy)
What mass do you use in neutralisation caliometry
Use vol of both solutions combined
What mass do you use in displacement caliometry
Only use vol of the solvent/liquid
What mass do you use for combustion caliometry
Mass of Water
