Enthalpy Changes Flashcards
(21 cards)
What are standard conditions?
100kPa
298k
In terms on energy describe an endothermic reaction
When energy is taken in from the surroundings, the enthalpy change is positive. This is an endothermic reaction
More energy is required when breaking bonds, than energy released when forming bonds.
In terms on energy describe an exothermic reaction.
when energy is released into the surroundings enthalpy change is negative. This is an exothermic reaction
More energy is released by forming g bonds than energy required when breaking bonds.
What is activation energy?
The minimum energy required for a reaction to take place between two colliding reactant particles.
Draw an enthalpy profile diagram for an exothermic reaction
Check pmt
Draw an enthalpy profile diagram for an endothermic reaction
Check pmt
Define the enthalpy change of reaction
The enthalpy change associated with a stated reaction. Quantities of substances in standard states react completely under standard conditions.
Define Enthalpy change of formation
The enthalpy change when one mole of a substance is produced from its elements in their standard states under standard conditions.
Define enthralls change of combustion?
the enthalpy change when one mole of a substance is burned completely in oxygen under standard conditions.
Deine enthalpy change of neutralisation.
The enthalpy change when solutions of acid and alkali react together under standard conditions to produce one mole of water.
Define average bond enthalpy
The energy required to break one mole of gaseous bonds. (Actual bond enthalpies may differ from the average bond enthalpy as the average bond enthalpy considers a particular bond in a range of molecules)
Define standard state.
The physical state of a substance under standard conditions.
What is calorimetry?
Experimental method for finding enthalpy change, which works by measuring temperature change over time. (When recorded and plotted on a graph data can be extrapolated to the exact point a reaction starts, giving a more accurate value for the change in temperature.)
Why are ΔH values found by using calorimetry never completely accurate?
Since energy is easily lost from the system, heat loss can occur due to conduction, convection or inaccuracies in measuring temperature.
How can heat loss be reduced where using calorimetry?
Can be reduced by putting a lid on the calorimeter and insulating the outsides of the calorimeter, using an insulator like polystyrene.
Define catalyst
Increases the rate of reaction without being used up in the reaction. (Works by prioviding an alternative reaction path with a lower activation energy).t
Why are catalysts used in industry?
Lower energy costs - lower temperatures and pressures to be used, whilst achieving the same rate of reaction.
Increases sustainability as well, as reduces energy demands for fossil fuels as it doesn’t require high temperatures.
What are homogenous catalysts?
Catalysts in the same phase as the reactants.
What are heterogenous catalysts?
Catalysts that are in a different phase to the species in the reaction, an example of this is the haber process where a solids iron catluyst is used to speed up the reaction.
Define adsorption
A solid catalyst works by adsorbing molecules onto an active site. On the surface of the catalyst. These active sites increase the proximity of molecules and weaken the covalent bonds in the molecules so that reactions occur more easily and the rate is increased. These catalysts are used ini industry to give surface for the reaction to occur on.
Define Le Chatelieur’s principle.
When a system is subject to a change in conditions, the position of equilibrium will shift to lessen the effect of that change.
