energetics
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what is enthalpy change
heat change at a constant pressure
what are the standard conditions
100KPa, 298K
what is an endothermic reaction
one that absorbs energy from the surroundings (temp decreases) (+ve)
what is temperature
a measure of the average kinetic energy of a particle in a system the faster the particles move the greater their kinetic energy, temp increase
what is heat
a measure of the total energy of all particles present in a given amount of any substance
what is a -ve enthalpy change reaction
exothermic
what is a +ve enthalpy change reaction
endothermic
what is standard enthalpy change
the heat change measured in standard conditions with all reactants and products in their standard states
what is standard enthalpy of combustion
The enthalpy change when one mole of an element or compound is completely burned in oxygen under standard conditions, with all reactants and elements in their standard states
what are the products of complete combustion
CO2 and H2O
what is standard enthalpy of formation
The enthalpy change when one mole of a compound is formed from its elements under standard conditions, with all reactants and products in their standard states
what is the equation for heat energy change (q)
q=mc(change in temp) m = the mass of the water/solution c = specific heat capacity of water 4.31J/Kg delta T = the temperature change (K)
why are results less exothermic than quoted data values
• heat loss to surroundings • incomplete combustion may take place • some heat energy is used to heat calorimeter • some fuel may have evaporated
why use a bomb calorimeter
it ensures complete combustion takes place as fuels burnt with oxygen well insulated which prevents heat loss
what is standard enthalpy of neutralisation
the enthalpy change when solutions of an acid and an alkali react together under standard conditions to produce one mole of water
what is Hess’s Law
The enthalpy change for a reaction, is the same whatever route is taken to get from reactants to products
what is bond dissociation enthalpy
the enthalpy required to break a particular covalent bond in a molecule when all species are in the gaseous state
what is mean bond enthalpy
average value of bond dissociation enthalpy of a particular type of bond in a range of different compounds
what is calorimetry
the process of measuring the amount of energy abosrbed or released during a chemical reaction