[{"data":1,"prerenderedAt":143},["ShallowReactive",2],{"reference-energy-diagrams":3},{"table":4},{"id":5,"slug":6,"title":7,"shortTitle":8,"category":9,"description":10,"metaDescription":11,"chart":12,"columns":84,"rows":104,"entryCount":122,"source":123,"notes":125,"relatedTopics":131,"relatedElements":134,"seoKeywords":135},22,"energy-diagrams","Reaction-Energy Diagrams: Activation Energy, ΔH, and Catalysis","Energy Diagrams","Kinetics","The four reaction-coordinate diagrams every kinetics student needs to read: an exothermic reaction, the same reaction catalyzed (lower Ea, same ΔH), an endothermic reaction, and a two-step mechanism with a rate-determining step. Activation energies and ΔH are annotated on each diagram and tabulated below.","Reaction energy diagram reference: activation energy, transition states, ΔH, catalyzed vs uncatalyzed pathways, and multi-step mechanisms with rate-determining steps - with annotated diagrams.",{"type":6,"diagrams":13},[14,37,50,63],{"key":15,"title":16,"caption":17,"payload":18},"uncatalyzed","Exothermic reaction (uncatalyzed)","The forward activation energy Ea is the climb from the reactant plateau to the transition state; ΔH is the net drop to the products. This is the graded Topic 20 diagram.",{"mode":19,"energy_unit":20,"reactants":21,"transition_state":24,"products":27,"annotations":30},"single_step","kJ",{"energy":22,"label":23},10,"Reactants",{"energy":25,"label":26},35,"TS",{"energy":28,"label":29},5,"Products",[31,34],{"type":32,"label":33},"ea_arrow","Ea",{"type":35,"label":36},"delta_h_arrow","ΔH",{"key":38,"title":39,"caption":40,"payload":41},"catalyzed","The same reaction with a catalyst","A catalyst provides a lower-energy pathway: the transition state drops, so Ea shrinks in BOTH directions, but the endpoints (and therefore ΔH) do not change. This is the graded Topic 20 comparison diagram.",{"mode":19,"energy_unit":20,"reactants":42,"transition_state":43,"products":45,"annotations":46},{"energy":22,"label":23},{"energy":44,"label":26},20,{"energy":28,"label":29},[47,49],{"type":32,"label":48},"Ea (catalyzed)",{"type":35,"label":36},{"key":51,"title":52,"caption":53,"payload":54},"endothermic","Endothermic reaction","Products sit ABOVE reactants: ΔH is positive, and the reverse activation energy is smaller than the forward one (Ea,rev = Ea,fwd − ΔH). Illustrative schematic.",{"mode":19,"energy_unit":20,"reactants":55,"transition_state":56,"products":58,"annotations":60},{"energy":28,"label":23},{"energy":57,"label":26},45,{"energy":59,"label":29},30,[61,62],{"type":32,"label":33},{"type":35,"label":36},{"key":64,"title":65,"caption":66,"payload":67},"two_step","Two-step mechanism (step 1 rate-determining)","A two-step mechanism shows one valley (the intermediate) between two transition states. The step with the largest activation barrier (here the first) is rate-determining. Illustrative schematic.",{"mode":68,"energy_unit":20,"reactants":69,"steps":70,"products":82},"multi_step",{"energy":22,"label":23},[71,78],{"transition_state":72,"intermediate":75},{"energy":73,"label":74},50,"TS₁",{"energy":76,"label":77},25,"Intermediate",{"transition_state":79},{"energy":80,"label":81},40,"TS₂",{"energy":83,"label":29},0,[85,89,92,95,98,101],{"key":86,"label":87,"type":88},"diagram","Diagram","text",{"key":90,"label":91,"type":88},"character","Character",{"key":93,"label":94,"type":88},"eaFwd","Ea (forward)",{"key":96,"label":97,"type":88},"eaRev","Ea (reverse)",{"key":99,"label":36,"type":100},"dH","chem",{"key":102,"label":103,"type":88},"barriers","Step Barriers",[105,111,114,118],{"diagram":16,"character":106,"eaFwd":107,"eaRev":108,"dH":109,"barriers":110},"Exothermic","25 kJ","30 kJ","−5 kJ","—",{"diagram":39,"character":106,"eaFwd":112,"eaRev":113,"dH":109,"barriers":110},"10 kJ","15 kJ",{"diagram":52,"character":115,"eaFwd":116,"eaRev":113,"dH":117,"barriers":110},"Endothermic","40 kJ","+25 kJ",{"diagram":65,"character":106,"eaFwd":116,"eaRev":119,"dH":120,"barriers":121},"50 kJ","−10 kJ","step 1: 40; step 2: 15",4,{"label":124},"ChemWhiz course diagrams (the catalysis pair is the graded Topic 20 payload set; the endothermic and two-step diagrams are labeled teaching schematics)",[126,127,128,129,130],"Reading the diagram: the forward activation energy Ea is the climb from the reactant plateau to the (highest) transition state; ΔH is the difference between product and reactant plateaus; and Ea,reverse = Ea,forward − ΔH.","A catalyst lowers the transition state, shrinking Ea in both directions and speeding both forward and reverse reactions equally, but it never changes ΔH or the equilibrium constant.","Exothermic: products below reactants (ΔH negative, heat released). Endothermic: products above reactants (ΔH positive, heat absorbed). The sign of ΔH says nothing about the RATE; that is Ea's job.","In a multi-step mechanism, each step has its own barrier measured from its own starting plateau; the step with the largest barrier is rate-determining. Valleys between transition states are intermediates: real species with finite lifetimes, unlike transition states.","The energy values on the schematics are illustrative; ChemWhiz problems supply their own diagram values in the problem statement.",[132,133],"chemical-kinetics","thermochemistry",[],[136,137,138,139,140,141,142],"reaction energy diagram","activation energy diagram","reaction coordinate diagram","catalyzed vs uncatalyzed energy diagram","rate determining step diagram","exothermic endothermic energy diagram","transition state intermediate",1785108608701]