thermodynamics (energetics) Flashcards
bomb calorimeter
the most accurate instrument for measuring the heat changes during combustion reactions
bond dissociation enthalpy
the enthalpy required to breaks one mole of covalent bond, with all species in the gaseous state; always endothermic
calorimeter
an instrument for measuring the heat changes that accompany chemical reactions
cooling curve
a graph of temperature vs time; used in calorimeter to compensate for heat loss
endothermic
a chemical reaction in which heat is taken in as reactants change to products; the temp drops. Bond breaking is endothermic
enthalpy change
the heat energy change at constant pressure
enthalpy / energy profile diagram
diagrams in which the enthalpies of reactants and products are products are plotted on a vertical scale to show their relative levels
enthalpy of neutralisation
the enthalpy change for the formation of one mole of water vus an acid - base reaction
enthalpy of reaction
the enthalpy change for given chemical reactions
exothermic
a chemical reaction in which heat is given out as reactants change to products; the temperature rises. Bond forming is exothermic
first law of thermodynamics
energy cannot be created nor destroyed, only change from one form to another
heat capacity
the amount of heat required to raise the temperature of substance by 1K; units of JK-1
hess law
the enthalpy change of a reaction is independent of the route taken
mean bond enthalpy
the value of the bond dissociation enthalpy for a given gaseous bond, averaged over many compounds in which the bond exists
specific heat capacity
the amount of heat required to raise the temperature of 1g of a substance by 1K
standard conditions
pressure of 1 atmosphere (101kPa) a stated temperature
standard enthalpy of combustion
the enthalpy change when 1 mole of a substance is completely burned in excess oxygen under standard conditions
standard enthalpy of formation
the enthalpy change when 1 mole of a substance is formed from its elements under standard conditions, all reactants and products in their standard states.
standard state
most stable physical state (solid, liquid or gas) of a substance at 101kPa and a stated temperature, usually 298K
surroundings
the environment in which a chemical reaction takes place
system
the reaction mixture only
thermochemical / hess cycle
a sequence of chemical reactions, with their enthalpy changes, that convert a reactant into a product. the total enthalpy change of the sequence of reactions will be the same as that for the conversion of the reactants to the products directly
one reason why the bond enthalpy that you calculated is diff from the mean bond enthalpy in the book
data book value derived from different compounds
how to determine a more accurate value for enthalpy of reaction
- use a polystyrene cup or a lid to reduce heat loss
-Record the temperature for a suitable time before
adding the metal
To establish an accurate initial temperature
Extrapolate the cooling back to the point of addition
To establish a (theoretical) maximum temperature
