6.2 Activation Energy

amount of energy needed for the reaction=

less energy- faster chemical reaction

what are the "hills" of the graph?

transition state

heat energy

- activation energy typically comes from heat energy from the surroundings -heat energy the total bond energy of the reactants or products in a chemical reaction speeds up the molecules' motion, increasing the frequency and force with which they collide - by moving atoms and bonds within the molecule,heat energy, helps reactions reach their transition state

endothermic reaction chart

- chemical reactions that absorb heat energy from the surroundings - temperature decreases with the progression of this reaction - enthalpy (heat energy) of the reactants is lower than that of the products change in enthalpy △H, is a positive value - energy should be absorbed or given to the system - heat content of a system at a constant pressure

exothermic reaction chart

- chemical reactions that release hear energy to the surroundings - temperature increases with progression of the reaction - enthalpy of reactants is higher than that of the products - change in enthalpy △H, is a negative value - energy is released from the system - it is the systems total energy

endothermic reaction graph explained

- energy is absorbed - the reactants start with a lower energy than the products end with because energy is absorbed - reactants have a lower energy than the products -△H is positive

exothermic reaction with activation energy graph explained

- energy of the reactants is higher than the products - activation energy is used to start the chemical reaction bringing you to the hump - energy is released during this chemical reaction leaving your products with less energy - the energy released is in the form of heat - △H is negative - warm to the touch

endothermic reaction with activation energy graph epxlained

- energy of the reactants is lower than the energy of the products - activation energy is used to start the chemical reaction bringing you to the hump - some of that activation energy is stored during the chemical reaction leaving the products with more energy - △H is positive - cold object

Change in enthalpy or △H

- for an endothermic graph it goes from reactants to products - for an exothermic graph it goes from products to reactants - measurement of △H overall to the △Hrxn - △H= + means endothermic △H= - means exothermic - enthalpy is heat transfer

catalysts job

- most chemical reactions that occur in living cells do NOT occur spontaneously - Kickstart chemical reactions and speed them up enabling cells to get the most out of the energy sources they have - life would be too slow without them - DO NOT participate in the chemical reaction Catalyst- a molecule which lowers the activation energy and allows a reaction to more readily occur

transition state

- the point of the reaction where there is the maximum amount of potential energy - where old bonds are broken (reactants) and new bonds are formed (products) - only way to make or form new products - a small energy input is required to achieve the transition state

exothermic reaction graph explained

- the reactants release energy to get to the products - the reaction starts with higher energy than it finishes with, thus the reactants have more energy than the products - has a negative enthalpy change or △H

activation energy in a graph explained

- there is the original activation energy needed to start the chemical reaction from the reactants, but the supply runs out (Ea,1) - it then reaches and intermediate low on energy where a second activation energy occurs to get the chemical reaction to its products (Ea, 2) - the total amount of activation energy used/ needed is measured on the biggest hump (Ea, overall) - remember activation energy is the energy you need to "climb a Hill" - it is measured in joules or kJ - this graph represents an exothermic reaction

enthalpy in a graph explained

- you measure the enthalpy by measuring the distance in energy from reactants to the products - since this is an exothermic reaction, energy is being released, the enthalpy change will be negative

catalyst definition

-a molecule that lowers the activation energy and allows a reaction to more readily occur - lowering the activation energy speeds up the process because it takes less energy input to start a chemical reaction with the catalyst

examples of endothermic reactions

-photosynthesis because heat (energy) is absorbed from the sun by plants - anytime energy is absorbed in the form of heat, but the substance feels cold - dissolving salt in water because the system has to take in the (energy) from its surroundings to break the bonds between the salt for it to dissolve

Activation energy or EA

-the minimum energy needed to start a chemical reaction -ex-lighter supplies the activation energy to make wood burn formula- reactants--> reactants and activation energy--> products ( effective collision)

examples of exothermic reactions

-water and acid reaction because the reaction releases heat (energy) -campfire because combination of oxygen, heat, and fuel creates a fire releasing heat (energy) - rusting nuclear fission because the rust producing process between iron and damp air releases a lot of heat (energy) - freezing water into ice because when water becomes a solid it releases heat warming up its surroundings

What type of reaction is this based on the amount of Delta G ( free energy) for the reactants and the products?

HINT- from reactants to products- AKA - the energy barrier it is an exergonic reaction

endothermic reactions

a reaction in which the system absorbs energy from its surroundings in the form of heat

rxn

abbreviation for reaction

exergonic reaction fig 6.10

activation energy is the energy required for a reaction to proceed, and it is lower if the reaction is catalyzed. This diagrams horizontal axis describes the sequence of events in time

what reaction would energy be stored? Would enthalpy be negative or positive?

endothermic positive

activation energy examples

flam, spark, radiation, high temperature

Delta H (change in enthalpy)....

is not affected by the catalyst only the activation energy

where does the transition state exist in the reaction?

it exists at a higher energy state than the reactants, thus Ea (activation energy) is always positive

high- energy, unstable state

molecules do not last long here "crystalized" elements

catalysts=

physically brings the reactants together= faster

Is the transition state closer in energy to the products or reactants? Endothermic? Exothermic? What kind of reaction would occur if the reactants literally have the same energy as the products?

reactants products reactants the reaction would be equilibrium because they both have the same amount of energy. A chemical reaction still occurs, but is not noticeable because of the equilibrium state they are in

heat energy

the total bond energy of the reactants or products in a chemical reaction speeds up the molecules' motion, increasing the frequency and force with which they collide

remember....

•Heating a system will cause chemical reactants within that system to react more frequently. •Increasing the pressure on a system also has the same effect! •Once reactants have absorbed enough heat energy from their surroundings to reach the transition state, the reaction will proceed.

activation energy=

"energy speed bump"- need more of it to complete the reaction which takes time

exothermic reactions

a reaction that releases energy from the system in the form of heat