Energetics I Flashcards
what is the standard enthalpy change of a reaction?
the enthalpy change when the reaction occurs in molar quantities shown in the chemical equation under standard conditions.
what is the standard enthalpy change of a reaction?
the enthalpy change when the reaction occurs in molar quantities shown in the chemical equation under standard conditions.
what is the standard enthalpy change of information?
the enthalpy change when 1 mol of a compound is formed from its elements in their standard rates under standard conditions.
what is the standard enthalpy change of combustion?
the enthalpy change when 1 mol of a substance is completely burned in oxygen under standard conditions.
what is the standard enthalpy of neutralisation?
the enthalpy change when an acid and an alkali react together under standard conditions to form 1 mol of water.
what is enthalpy change?
the heat energy change in a reaction at constant pressure. the units are kjmol-1
what are standard conditions?
1atm 298k
what is the energy change in an exothermic reaction?
the reaction gives out heat and therefore it is negative (the temperature goes up)
what is the energy change in an endothermic reaction?
reactions absorb energy and so the change is positive (the temperature usually falls)
what do you need to calculate the enthalpy of a reaction?
the number of moles that are reacting
the change in temperature of the reaction.
what do you need to find the enthalpy changes of combustion?
you need a calorimeter. to find the enthalpy of a flammable liquid you burn it. as the fuel burns it heat the water. you can work out the heat absorbed by the water if you know the mass of the water, the temperature change of the water and the specific heat capacity of the water
what is hess’s law?
the total enthalpy change of a reaction is always the same, no matter which rout is taken.
how do you calculate hess’s law
sum of clockwise enthalpy = sum of anticlockwise
what is bond enthalpy?
the amount of energy required to break 1 mol of a type of bond in a molecule in the gas phase.
what heat change is seen when breaking and making bonds?
energy is needed to break bonds so breaking binds is endothermic (positive)
energy is given out when bonds are formed so this is exothermic (negative)
