energy (bond energy and in the natural world)

photosynthesis

• formation of carbohydrates (C6H12O6), oxygen

• formed by CO2(g), H2O(l), sunlight energy

• catalyzed by chlorophyll in green parts of plant

• 6 CO₂_(g) + 6 H₂O_(l) + energy → C₆H₁₂O₆_(aq) + 6 O₂_(g)

photosynthesis energy diagram

• reactants have less chemical potential energy than products

• endothermic

• energy is a reactant

• Δ_rH is positive

cellular respiration

• reverse of photosynthesis

• organisms take in glucose, oxygen gas

• produce CO2(g), H2O(l), ATP

• C₆H₁₂O₆_(aq) + 6 O₂_(g) → 6 CO₂_(g) + 6 H₂O_(l) + energy

cellular respiration energy diagram

• heat released in small amounts - liquid

• exothermic

• energy is a product

• reactants have more chemical potential energy than products

• Δ_rH is negative

combustion

• hydrocarbons burned in presence of oxygen

• produce CO2, H2O(g)

• x Hydrocarbon + x O₂_(g) → x CO₂_(g) + x H₂O_(g)

combustion energy diagram

• heat released in large amounts - vapour

• exothermic

• energy is a product

• reactants have more chemical potential energy than products

• Δ_rH is negative

cellular respiration vs complete combustion

cellular respiration releases more energy than complete combustion

collision theory

• chemical reaction needs particles to collide in the correct orientation and enough energy

• needs more collisions to increase rate of reaction

effective collision

• correct orientation

• enough energy

• chemical reaction

ineffective collision

• wrong orientation

• not enough energy

• no chemical reaction

increasing collisions

• increase temperature

• increase surface area

• increase concentration

• introduce catalyst

• decrease volume

increase temperature

speed up molecules to increase energy

increase surface area

increase area for proper orientation

increase concentration

increase number of molecules

introduce a catalyst

increases rate of reaction

decrease volume

decrease distance molecules travel

activation energy

minimum energy required to initiate a reaction by breaking bonds in the reactants

Boltzmann Distribution Curve

• distribution of energy at certain temperatures

• E_A line: at or above, molecules have enough energy for collision

• green: ineffective collisions, not enough eenrgy

• blue: enough energy - reaction

Boltzmann Distribution Curve change in temperature

• result in an increase in average energy of molecules and rate of reaction

• more collisions - particles gain kinetic energy, move faster

• molecules have higher kinetic energy than activation energy

bond breaking

• heat taken from surroundings

• endothermic

bond making

• heat released to surroundings

• exothermic

endothermic

• energy needed to break bonds is greater than energy released

• positive enthalpy

exothermic

• energy released to form bonds is greater than energy taken in

• negative enthalpy

Reaction Pathway Diagrams

• x axis: energy of reactants

• y axis: energy of products

• activation energy - high kinetic energy (bump in graph)

creating Reaction Pathway Diagrams

1. balance chemical equation

2. exothermic or endothermic

3. draw curve for transition state

4. draw arrows for activation energy and enthalpy values