module 3 - enthalpy changes Flashcards
- what is enthalpy?
- what’s the symbol for enthalpy?
- a measure of the heat energy in a chemical system
- H
what can enthalpy sometimes be thought of as being?
the energy stored within bonds
how is enthalpy measured?
it can’t be measured, so enthalpy change is measured
what is enthalpy change?
the difference between the enthalpy of the products and the enthalpy of the reactants
what equation works out enthalpy change?
enthalpy of products —- enthalpy of reactants = enthalpy change
what is the system?
the reactants and products
what are the surroundings?
the apparatus , the lab and everything outside the system
what is the universe?
everything, including system and surroundings
how can enthalpy change be determined?
experimentally by measuring energy transfer between system and surroundings
what does activation energy act as in chemical reactions?
a barrier
what is activation energy?
the minimum energy required to start a reaction by the breaking of bonds
do reactions with small or large activation energies happen more rapidly? why?
- small
- because the energy needed to break bonds is readily available from the surroundings
what’s the unit for enthalpy change?
kj mol ^-1
what are standard conditions for standard state?
- 100 kpa
- 298k
what is the standard enthalpy change of reaction?
the enthalpy change that accompanies a reaction in the molar quantities shown in an equation under standard conditions, with all reactants and products in their standard states
