[{"data":1,"prerenderedAt":167},["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":105,"rows":125,"entryCount":143,"source":144,"notes":146,"relatedTopics":152,"relatedElements":155,"seoKeywords":156,"tableTitle":164,"tableDescription":165,"seoTitle":166},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 diagrams: activation energy, transition states, ΔH, and how a catalyst lowers the barrier, for exo- and endothermic reactions.",{"type":6,"comparisonNote":13,"diagrams":14},"Compare the first two diagrams on the same 0–40 kJ scale: the catalyst lowers the transition-state energy while the reactant and product levels stay fixed.",[15,45,60,75],{"key":16,"title":17,"caption":18,"displayConfig":19,"payload":26},"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.",{"width":20,"height":21,"show_gridlines":22,"energy_min":23,"energy_max":24,"curve_color":25},420,300,true,0,40,"#2563eb",{"mode":27,"energy_unit":28,"reactants":29,"transition_state":32,"products":35,"annotations":38},"single_step","kJ",{"energy":30,"label":31},10,"Reactants",{"energy":33,"label":34},35,"TS",{"energy":36,"label":37},5,"Products",[39,42],{"type":40,"label":41},"ea_arrow","Eₐ",{"type":43,"label":44},"delta_h_arrow","ΔH",{"key":46,"title":47,"caption":48,"displayConfig":49,"payload":51},"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.",{"width":20,"height":21,"show_gridlines":22,"energy_min":23,"energy_max":24,"curve_color":50},"#16a34a",{"mode":27,"energy_unit":28,"reactants":52,"transition_state":53,"products":55,"annotations":56},{"energy":30,"label":31},{"energy":54,"label":34},20,{"energy":36,"label":37},[57,59],{"type":40,"label":58},"Eₐ (catalyzed)",{"type":43,"label":44},{"key":61,"title":62,"caption":63,"displayConfig":64,"payload":66},"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.",{"width":20,"height":21,"show_gridlines":22,"energy_min":23,"energy_max":65,"curve_color":25},50,{"mode":27,"energy_unit":28,"reactants":67,"transition_state":68,"products":70,"annotations":72},{"energy":36,"label":31},{"energy":69,"label":34},45,{"energy":71,"label":37},30,[73,74],{"type":40,"label":41},{"type":43,"label":44},{"key":76,"title":77,"caption":78,"displayConfig":79,"payload":83},"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.",{"width":20,"height":21,"show_gridlines":22,"energy_min":80,"energy_max":81,"curve_color":82},-5,55,"#7c3aed",{"mode":84,"energy_unit":28,"reactants":85,"steps":86,"products":96,"annotations":97},"multi_step",{"energy":30,"label":31},[87,93],{"transition_state":88,"intermediate":90},{"energy":65,"label":89},"TS₁ (RDS)",{"energy":91,"label":92},25,"Intermediate",{"transition_state":94},{"energy":24,"label":95},"TS₂",{"energy":23,"label":37},[98,101,104],{"type":99,"step_index":23,"label":100},"step_ea_arrow","Eₐ,1",{"type":99,"step_index":102,"label":103},1,"Eₐ,2",{"type":43,"label":44},[106,110,113,116,119,122],{"key":107,"label":108,"type":109},"diagram","Diagram","text",{"key":111,"label":112,"type":109},"character","Character",{"key":114,"label":115,"type":109},"eaFwd","Eₐ (forward)",{"key":117,"label":118,"type":109},"eaRev","Eₐ (reverse)",{"key":120,"label":44,"type":121},"dH","chem",{"key":123,"label":124,"type":109},"barriers","Step Barriers",[126,132,135,139],{"diagram":17,"character":127,"eaFwd":128,"eaRev":129,"dH":130,"barriers":131},"Exothermic","25 kJ","30 kJ","−5 kJ","—",{"diagram":47,"character":127,"eaFwd":133,"eaRev":134,"dH":130,"barriers":131},"10 kJ","15 kJ",{"diagram":62,"character":136,"eaFwd":137,"eaRev":134,"dH":138,"barriers":131},"Endothermic","40 kJ","+25 kJ",{"diagram":77,"character":127,"eaFwd":137,"eaRev":140,"dH":141,"barriers":142},"50 kJ","−10 kJ","step 1: 40; step 2: 15",4,{"label":145},"ChemWhiz kinetics reference diagrams; the endothermic and two-step examples are teaching schematics",[147,148,149,150,151],"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 ΔH = Eₐ (forward) − Eₐ (reverse).","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 teaching values.",[153,154],"chemical-kinetics","thermochemistry",[],[157,158,159,160,161,162,163],"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","Activation Energy and ΔH by Diagram","Compare the forward and reverse activation energies, the sign of ΔH, and how a catalyst lowers Ea.","Reaction-Energy Diagrams",1787246032948]