energy and catalysts

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

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

Catalyst

• rate of a chemical reaction is increased

• providing reactants with alternative reaction pathway

• decrease activation energies

catalyst process

• molecule binds catalyst

• increased rate of disociation

• released from catalyst (catalyst has not changed shape)

positive catalyst

• increase rate of reaction

• decrease activation energy

• accept smaller energetic pathway

negative catalyst

• decrease rate of reaction

• increase activation energy

• less effective collisions

examples of catalysts

enzymes

• catalyze reactions in living cells

Heterogeneous Catalysts in Catalytic Converters

• nitrogen oxide → nitrogen gas

• carbon monoxide → carbon dioxide

transition state

chemical bonds are partially broken and formed

Reaction pathway diagram

• A: potential energy of reactants

• B: potential energy of transition state

• C: energy of activation (forward reaction)

• D: energy of activation (reverse reaction)

• E: potential energy of product

• F: enthalpy change