{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"equilibrium-constant"},"result":{"entity_type":"calculator","id":"equilibrium-constant","calculator_id":"equilibrium-constant","canonical_url":"https://tttkmbb.com/chemistry/equilibrium-constant","name":"Equilibrium Constant Calculator","title":"Equilibrium Constant Calculator – Kc from Equilibrium Concentrations, Kp = Kc(RT)^Δn and ΔG° = −RT ln K","category":"chemistry","category_name":"Chemistry","tool_name":"calculate_equilibrium_constant","featured_mcp_tool":false,"description":"Computes the concentration equilibrium constant Kc of a reaction aA + bB ⇌ cC + dD from equilibrium concentrations raised to their stoichiometric coefficients, converts it to Kp with Kp = Kc·(RT)^Δn for gas-phase reactions, and reports log K, the standard Gibbs energy ΔG° = −RT·ln K and which side the equilibrium favours.","use_when":"You have equilibrium concentrations of the species of a balanced reaction with up to two reactants and two products and need Kc, Kp, ΔG° or a statement of whether products or reactants are favoured.","do_not_use_when":"You need to predict equilibrium concentrations from a known K and initial amounts (an ICE-table problem), the pH of a weak acid (use weak-acid-ph), or K from a cell potential (use nernst-equation).","inputs":[{"name":"coefficient_a","label":"Coefficient a (reactant A)","type":"integer","required":false,"default":1,"min":1,"max":20,"description":"Stoichiometric coefficient of reactant A.","example":1},{"name":"concentration_a","label":"[A] at equilibrium","type":"number","unit":"mol/L","required":true,"max":1000000,"exclusive_min":0,"description":"Equilibrium concentration of reactant A (omit pure solids, liquids and the solvent from the expression by not entering them).","example":0.1},{"name":"coefficient_b","label":"Coefficient b (reactant B)","type":"integer","required":false,"default":0,"min":0,"max":20,"description":"Stoichiometric coefficient of reactant B; 0 when there is no second reactant.","example":1},{"name":"concentration_b","label":"[B] at equilibrium","type":"number","unit":"mol/L","required":false,"default":0,"min":0,"max":1000000,"description":"Equilibrium concentration of reactant B (required when coefficient_b > 0).","example":0.1},{"name":"coefficient_c","label":"Coefficient c (product C)","type":"integer","required":false,"default":1,"min":1,"max":20,"description":"Stoichiometric coefficient of product C.","example":2},{"name":"concentration_c","label":"[C] at equilibrium","type":"number","unit":"mol/L","required":true,"max":1000000,"exclusive_min":0,"description":"Equilibrium concentration of product C.","example":0.7},{"name":"coefficient_d","label":"Coefficient d (product D)","type":"integer","required":false,"default":0,"min":0,"max":20,"description":"Stoichiometric coefficient of product D; 0 when there is no second product.","example":0},{"name":"concentration_d","label":"[D] at equilibrium","type":"number","unit":"mol/L","required":false,"default":0,"min":0,"max":1000000,"description":"Equilibrium concentration of product D (required when coefficient_d > 0).","example":0},{"name":"temperature_k","label":"Temperature","type":"number","unit":"K","required":false,"default":298.15,"max":100000,"exclusive_min":0,"description":"Absolute temperature used for Kp = Kc(RT)^Δn and ΔG° = −RT ln K (298.15 K = 25 °C).","example":298.15}],"outputs":[{"name":"kc","label":"Kc","type":"number","decimals":10,"description":"[C]^c [D]^d / ([A]^a [B]^b) with concentrations in mol/L (dimensionless by convention)."},{"name":"kc_scientific","label":"Kc (scientific)","type":"string","decimals":4,"description":"Kc in scientific notation."},{"name":"kp","label":"Kp","type":"number","decimals":10,"description":"Kc × (R·T)^Δn with R = 0.082057 L·atm/(mol·K): the pressure-based constant with partial pressures in atm (equal to Kc when Δn = 0)."},{"name":"kp_scientific","label":"Kp (scientific)","type":"string","decimals":4,"description":"Kp in scientific notation."},{"name":"delta_n_gas","label":"Δn (gas)","type":"integer","decimals":4,"description":"c + d − a − b: change in moles of gas per reaction as written."},{"name":"rt_l_atm_per_mol","label":"R·T","type":"number","unit":"L·atm/mol","decimals":4,"description":"0.082057 × temperature_k, the factor raised to Δn."},{"name":"log_kc","label":"log10 Kc","type":"number","decimals":4,"description":"Base-10 logarithm of Kc."},{"name":"delta_g_kj_mol","label":"ΔG° from Kc","type":"number","unit":"kJ/mol","decimals":3,"description":"−R·T·ln Kc with R = 8.314 J/(mol·K), standard state 1 mol/L; negative when products are favoured."},{"name":"delta_g_kp_kj_mol","label":"ΔG° from Kp","type":"number","unit":"kJ/mol","decimals":3,"description":"−R·T·ln Kp (standard state 1 atm), the value to use for gas-phase reactions; identical to delta_g_kj_mol when Δn = 0."},{"name":"reaction_direction","label":"Equilibrium position","type":"string","decimals":4,"description":"Whether products or reactants are favoured (K > 1, K < 1 or K ≈ 1)."},{"name":"reaction_text","label":"Reaction","type":"string","decimals":4,"description":"The reaction as interpreted, e.g. 1 A + 3 B ⇌ 2 C."}],"input_schema":{"type":"object","properties":{"coefficient_a":{"description":"Stoichiometric coefficient of reactant A.","type":"integer","minimum":1,"maximum":20,"default":1,"examples":[1]},"concentration_a":{"description":"Equilibrium concentration of reactant A (omit pure solids, liquids and the solvent from the expression by not entering them). Unit: mol/L.","type":"number","maximum":1000000,"exclusiveMinimum":0,"examples":[0.1],"x-unit":"mol/L"},"coefficient_b":{"description":"Stoichiometric coefficient of reactant B; 0 when there is no second reactant.","type":"integer","minimum":0,"maximum":20,"default":0,"examples":[1]},"concentration_b":{"description":"Equilibrium concentration of reactant B (required when coefficient_b > 0). Unit: mol/L.","type":"number","minimum":0,"maximum":1000000,"default":0,"examples":[0.1],"x-unit":"mol/L"},"coefficient_c":{"description":"Stoichiometric coefficient of product C.","type":"integer","minimum":1,"maximum":20,"default":1,"examples":[2]},"concentration_c":{"description":"Equilibrium concentration of product C. Unit: mol/L.","type":"number","maximum":1000000,"exclusiveMinimum":0,"examples":[0.7],"x-unit":"mol/L"},"coefficient_d":{"description":"Stoichiometric coefficient of product D; 0 when there is no second product.","type":"integer","minimum":0,"maximum":20,"default":0,"examples":[0]},"concentration_d":{"description":"Equilibrium concentration of product D (required when coefficient_d > 0). Unit: mol/L.","type":"number","minimum":0,"maximum":1000000,"default":0,"examples":[0],"x-unit":"mol/L"},"temperature_k":{"description":"Absolute temperature used for Kp = Kc(RT)^Δn and ΔG° = −RT ln K (298.15 K = 25 °C). Unit: K.","type":"number","maximum":100000,"exclusiveMinimum":0,"default":298.15,"examples":[298.15],"x-unit":"K"}},"additionalProperties":false,"required":["concentration_a","concentration_c"]},"output_schema":{"type":"object","properties":{"kc":{"description":"[C]^c [D]^d / ([A]^a [B]^b) with concentrations in mol/L (dimensionless by convention).","type":"number"},"kc_scientific":{"description":"Kc in scientific notation.","type":"string"},"kp":{"description":"Kc × (R·T)^Δn with R = 0.082057 L·atm/(mol·K): the pressure-based constant with partial pressures in atm (equal to Kc when Δn = 0).","type":"number"},"kp_scientific":{"description":"Kp in scientific notation.","type":"string"},"delta_n_gas":{"description":"c + d − a − b: change in moles of gas per reaction as written.","type":"integer"},"rt_l_atm_per_mol":{"description":"0.082057 × temperature_k, the factor raised to Δn. Unit: L·atm/mol.","type":"number","x-unit":"L·atm/mol"},"log_kc":{"description":"Base-10 logarithm of Kc.","type":"number"},"delta_g_kj_mol":{"description":"−R·T·ln Kc with R = 8.314 J/(mol·K), standard state 1 mol/L; negative when products are favoured. Unit: kJ/mol.","type":"number","x-unit":"kJ/mol"},"delta_g_kp_kj_mol":{"description":"−R·T·ln Kp (standard state 1 atm), the value to use for gas-phase reactions; identical to delta_g_kj_mol when Δn = 0. Unit: kJ/mol.","type":"number","x-unit":"kJ/mol"},"reaction_direction":{"description":"Whether products or reactants are favoured (K > 1, K < 1 or K ≈ 1).","type":"string"},"reaction_text":{"description":"The reaction as interpreted, e.g. 1 A + 3 B ⇌ 2 C.","type":"string"}}},"formula":"Kc = concentration_c^c × concentration_d^d / (concentration_a^a × concentration_b^b); Δn = c + d − a − b; Kp = Kc × (R × T)^Δn with R = 0.082057 L·atm/(mol·K); ΔG° = −R × T × ln K with R = 8.314 J/(mol·K); log_kc = log10 Kc","method":"Concentrations are used in place of activities, so K is dimensionless relative to the 1 mol/L (Kc) or 1 atm (Kp) standard state; species with coefficient 0 are omitted, as pure solids, liquids and the solvent should be. K is temperature-dependent: the entered temperature only converts Kc to Kp and to ΔG°, it does not extrapolate K to another temperature (that needs ΔH° via the van 't Hoff equation).","sources":[{"name":"Wikipedia – Equilibrium constant","url":"https://en.wikipedia.org/wiki/Equilibrium_constant","type":"reference","retrieved_at":"2026-09-24"},{"name":"OpenStax Chemistry 2e – 13.2 Equilibrium Constants","url":"https://openstax.org/books/chemistry-2e/pages/13-2-equilibrium-constants","type":"textbook","retrieved_at":"2026-09-24"},{"name":"IUPAC Gold Book – equilibrium constant","url":"https://goldbook.iupac.org/terms/view/E02177","type":"standard","retrieved_at":"2026-09-24"}],"freshness":{"type":"static","max_age_seconds":null,"note":"Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output."},"examples":[{"name":"H2 + I2 ⇌ 2 HI with [H2] 0.1, [I2] 0.1, [HI] 0.7 mol/L at 298.15 K","inputs":{"coefficient_a":1,"concentration_a":0.1,"coefficient_b":1,"concentration_b":0.1,"coefficient_c":2,"concentration_c":0.7},"expected":{"kc":49,"kp":49,"delta_n_gas":0,"log_kc":1.6902,"delta_g_kj_mol":-9.648,"reaction_direction":"K > 1: products favoured at equilibrium","reaction_text":"1 A + 1 B ⇌ 2 C"},"url":"https://tttkmbb.com/api/v1/calculate/equilibrium-constant?coefficient_a=1&concentration_a=0.1&coefficient_b=1&concentration_b=0.1&coefficient_c=2&concentration_c=0.7"},{"name":"N2 + 3 H2 ⇌ 2 NH3 at 500 K with Kc = 0.5 ([N2] 1, [H2] 1, [NH3] 0.70711)","inputs":{"coefficient_a":1,"concentration_a":1,"coefficient_b":3,"concentration_b":1,"coefficient_c":2,"concentration_c":0.70711,"temperature_k":500},"expected":{"kc":0.5,"delta_n_gas":-2,"kp":0.00029703,"kp_scientific":"2.970e-4","rt_l_atm_per_mol":41.0287,"delta_g_kj_mol":2.881,"delta_g_kp_kj_mol":33.764,"reaction_direction":"K < 1: reactants favoured at equilibrium","reaction_text":"1 A + 3 B ⇌ 2 C"},"url":"https://tttkmbb.com/api/v1/calculate/equilibrium-constant?coefficient_a=1&concentration_a=1&coefficient_b=3&concentration_b=1&coefficient_c=2&concentration_c=0.70711&temperature_k=500"}],"faq":[{"q":"How do I enter a reaction with a solid or the solvent?","a":"Leave it out: pure solids, pure liquids and water as solvent have activity 1 and do not appear in K. Set the unused coefficient to 0 (B or D) or renumber the species so A and C are the ones that appear."},{"q":"Kp in atm or bar?","a":"Kp here uses partial pressures in atm (R = 0.082057 L·atm/(mol·K)). For the IUPAC 1 bar standard state multiply by 1.01325^Δn, or equivalently use R = 0.083145 L·bar/(mol·K)."},{"q":"How does K change with temperature?","a":"This calculator does not extrapolate K. Use the van 't Hoff equation ln(K2/K1) = −(ΔH°/R)(1/T2 − 1/T1): K rises with temperature for endothermic reactions and falls for exothermic ones."}],"tags":["equilibrium constant","kc","kp","reaction quotient","gibbs free energy","law of mass action"],"related":[{"calculator_id":"nernst-equation","reason":"Equilibrium constant and ΔG° from a standard cell potential."},{"calculator_id":"ideal-gas-law","reason":"Convert between gas concentrations and partial pressures."},{"calculator_id":"weak-acid-ph","reason":"Ka is the equilibrium constant of acid dissociation."}],"links":{"html":"https://tttkmbb.com/chemistry/equilibrium-constant","markdown":"https://tttkmbb.com/chemistry/equilibrium-constant.md","json":"https://tttkmbb.com/chemistry/equilibrium-constant.json","api":"https://tttkmbb.com/api/v1/calculate/equilibrium-constant","schema":"https://tttkmbb.com/api/v1/calculators/equilibrium-constant","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-24T03:44:39Z"}