rates and energy differences Flashcards
Exothermic reaction
H(enthalpy)decreasesduring the reaction
➢Energy isreleased
➢Surroundings get hot
energy: H reactants>Hproducts
(bondsin the products have lessenthalpythan the bonds in the reactants)
Law of conservation of energy states thatenergy must be conserved
Therefore, Hreactants = H products + energy
Since energy is released,temp of surroundingsincrease
The difference in enthalpy between reactants and products = amount of energy releasedto the surroundings.
Exothermic reactions: ΔH= -ve (Enthalpy has decreased)
making bonds = releases energy
Exothermic reaction:energy required to break bonds is LESSthan the energy
released in the formation of new bonds. Therefore, energy is higher in the making of bonds.
(breaks bonds, then) makes bonds
heat moves from system into surroundings
In an exothermic reaction, the energy released when new bonds are formed is greater than the energy taken in breaking the existing bonds.
endothermic reaction
➢H increasesduring the reaction
➢Energy isabsorbed
➢Surroundings get cold
energy: H reactants <H products
(bondsin the products have more energy than the bonds in the reactants)
H reactants +energy =H products
Sinceenergy is absorbed,temp of surroundingsdecrease
Difference in enthalpy between reactants and products = amount of energy absorbed
Endothermic reactions: ΔH = +ve(Enthalpy has increased)
breaking bonds = requires energy
Endothermic reaction:energy required to break bonds is MOREthan the energy released in the formation of new bonds.
breaks bonds only
heat moves from surroundings into system
In endothermic reactions, the energy needed to break existing bonds is greater than the energy released when new bonds are formed.
Change in enthalpy (ΔH)
H products – H reactants
Exothermic reactions: ΔH
-ve (Enthalpy has decreased)
Endothermic reactions: ΔH
+ve(Enthalpy has increased)
Enthalpy (H)
stored chemical potential energy (kJ/mol)
Transition state
intermediate state where bond breaking and bond forming is occurring. Highest enthalpy state of the reaction.
Activation energy (Ea)
minimum amount of energy required for the reaction (bond breaking) to occur.
(difference between enthalpy of reactants and transition state)
FACTORS THAT AFFECT REACTION RATE:
- Catalysts
- concentration
- Increasing temperature
- state of subdivision
- nature of reactants
Catalysts
speed up reactions as it decreases activation energy!
A higher (reactant) concentration
increases rate of reaction as the particles are closer which increases likelihood for collisions(frequency of collisions) and so the reaction is more likely to occur, greater number of particles per unit volume → higher chance and frequency of more successful collisions = faster reaction rate (applies to substances as a solution or in the gaseous state)
Increasing temperature
(measure of average kinetic energy) results in a faster rate of reaction, this is as increasing the temperature increases the kinetic energy of the particles, which results in a greater number of collisions per unit time, which increases the number of successful collisions
state of subdivision
greater the surface area, more particles are able to be exposed to collisions, increased availability of particles increases likelihood for collisions (frequency of collisions) and so the reaction is more likely to occur, higher chance and frequency of more successful collisions = faster reaction rate
nature of reactants
covalent molecular reactions are slow as they involve the process of bond breaking and bond rearrangement, collisions are almost unsuccessful at room temp as there is insufficient activation energy
collision theory
individual particles of the reacting substances must collide
the collision energy must be greater than or equal to a certain minimum amount known as the activation energy
the reacting particles must collide with a suitable orientation (for bond breaking and bond forming to occur)
greater the rate of successful collisions → greater the reaction rate
