Energetics (3.1.4) Flashcards
what can reactions be?
endothermic or exothermic
what is enthalpy change (△H)?
the change in heat energy measured under conditions of constant pressure
what is standard pressure?
100 kPa
what is standard temperature?
the stated temperature, but usually 298 K
what is standard state?
the normal physical form of a substance under standard conditions eg. for carbon it is graphite
what is standard enthalpy change (∆HƟ)?
the change in enthalpy measured under standard conditions with all substances being in their standard states
what is the standard enthalpy of combustion (∆c H Ɵ)?
the enthalpy change when 1 mole of a substance reacts completely with oxygen under standard conditions with all substances being in their standard state
what is the balanced equation for the combustion of butanethiol (C4H9SH) where the enthalpy change is the standard enthalpy of combustion?
C4H9SH (l) + 7 1/2 O2 (g) -> 4 CO2 (g) + 5 H2O (g) + SO2 (g)
what do you need to remember for balancing equations for standard enthalpy of combustion?
there must only be one mole of the substance reacting with oxygen, so other balancing numbers may involve fractions (balance normally and then divide)
what is the standard enthalpy of formation (∆f H Ɵ )?
the enthalpy change when 1 mole of a substance is made from its elements under standard conditions with all substances being in their standard state
what is the balanced equation for the formation of butanethiol (C4H9SH) where the enthalpy change is the standard enthalpy of formation?
4 C (s) + 5 H2 (g) + S (s) -> C4H9SH (l)
what do you need to remember for balancing equations for standard enthalpy of formation?
the substance being formed should be the only product and there must only be one mole of it formed
how do you calculate the enthalpy change in a reaction?
q = m x c x ∆T
m = mass of substance
c= specific heat capacity
∆T = change in temperature
