Chapter 9 - Enthalpy Flashcards
what is enthalpy H?
a measure of the heat energy in a chemical system
What is enthalpy change 🔺H?
the difference in enthalpies of the products and reactants
how can 🔺H be calculated?
H(products) - H(reactants)
do exothermic products have a negative or positive 🔺H?
negative
do endothermic products have a negative or positive 🔺H?
positive
what is the activation energy Ea?
the minimum energy required for a reaction to take place
what is standard physical value and it’s units?
refers to a reaction under standard conditions, units are KJ mol ^-1
what is the enthalpy change of reactions 🔺rH🔴?
the enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions
what is the enthalpy change of formation 🔺fH🔴?
the enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions
what is the enthalpy change of combustion 🔺cH🔴?
the enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions
what is the enthalpy change of neutralisation 🔺neut H🔴?
the energy change that accompanies the reaction of an acid by a base to form one mole of H2O under standard conditions
what is the equation for heat energy q?
q= m c 🔺T
what is average bond enthalpy?
the energy required to break one mole of a specified type of a bond in a gaseous molecule
why can the actual bond enthalpy vary?
different chemical environnements
how can you calculate the enthalpy change of reaction 🔺rH?
🔺rH= { (bond enthalpies in reactants) - { (bond enthalpies in products)
what does Hess’ law state?
if a reaction can take place by two routes, and the starting and finishing conditions are the same, the total enthalpy change is the same for each route
what is the equation for enthalpy change using q?
-q / n
