3.2 Physical Chemistry Flashcards
(36 cards)
What is the law of conservation of energy?
Energy can not be created or destroyed only transferred, stored or dissipated
What’s an exothermic reaction?
Energy lost to surroundings,
reactants more energy than products (-ΔH )
What’s an endothermic reaction?
Energy taken in from surroundings,
products more energy than reactants (+ΔH)
What is activation energy?
The energy required to break bonds in the reactants
What are standard conditions?
100 Kpa (100,000 pa) ot 1 atm 298k(k=c°+ 273) 1 mol dm-3
What is enthalpy change of formation?
Energy change associated with formation of 1mol of compound from a substituent elements
What is enthalpy change of combustion?
Energy change that accompanies the COMPLETE combustion of 1 mol of a substance
What is enthalpy change of neutralisation?
Energy change associated with formation of 1mol of water from a neutralisation reaction
What equation links energy in joules, mass of substance& specific heat capacity?
q=mcΔT • q- energy in joules • m- mass of substance heated or cooled • c- specific heat capacity • ΔT- temperature change
What is average bond enthalpy?
The Mean energy needed for 1 mol of gaseous bonds to undergo homolytic fission
What is Hess law?
States regardless of the multiple stages or steps of a reaction, the total enthalpy change for the reaction is the sum of all changes
Hess cycle for formation
formation up
reactants → products
⇖ ⇗
sub elements
Hess cycle for combustion
combustion down
reactants → products
⇘ ⇙
combustion products
What is the equation for rate of reaction?
rate=change in conc/ time
units =mol dm3 s-1
What factors effect rate of reaction?
- Temperature
- surface area
- Concentration
- pressure (gaseous reactions only)
- catalyst (not for reversible)
What’s collision theory?
For a chemical reaction to take place molecules must collide with sufficient energy in the correct orientation
Effect of temp on exothermic reaction @ equilibrium?
- decrease temp favours forward (exo) reaction
* increase temp favours reverse reaction
Effect of temp on endothermic reaction @ equilibrium?
- increase temp favours forward (endo)reaction
* decrease temp favours reverse reaction
How does pressure effect a gaseous reaction @ equilibrium?
- increased pressure favours side with less gas mol
* decreased pressure favours side with more gas mol
How can we measure reaction rates?
- collect gas in syringe formed during reaction
- monitor reactions mass
- record time taken for certain change to occur
- calorimeter
What is a catalyst?
substances that increases the rate of reaction without being used up
What’s a Homogenous catalyst
Catalyst in same phase(state of matter) as reactants
What’s a Heterogenous catalyst
Catalyst in different phase(state of matter) as reactants
What’s the economic reasons for catalyst?
- lower energy demands (activation energy) for reactions
- less fuel used so less emissions
- speed up reactions
