Thermochemistry

Comparison of Combustion Heat of Difference Fuel The table below shows the heat of combustion of a few fuel. It shows that when the number of carbon in a molecule increase, the heat of combustion will increase. Alcohol MolecularFormula DH (kJ mol-1) Methanol CH3OH ‑715 Ethanol C2H5OH ‑1376 Propan-1-ol C3H7OH ‑2017 Butan-1-ol C4H9OH ‑2675 If … Read more

Combustion Combustion is a reaction when a substance burns completely in the excess oxygen. Example, combustion of methane in excess of oxygen produces carbon dioxide and water.CH4 + 2O2 → CO2 + 2H2O All fuel combustion are exothermic reactions. Heat of Combustion The Heat of Combustion of a substance is the heat energy released when 1 … Read more

The heat of neutralisation is the heat energy evolved when an acid reacts with a base, per mole of the acid or base. All measurements are made under standard state conditions. An example of the enthalpy change of neutralisation is the heat change obtained in the reaction between sodium hydroxide and hydrochloric acid. The equation … Read more

Heat of displacement is the energy change when one mole of metal is displaced from its salt solution by a more electropositive metal Displacement reaction occurs when a metal which is situated at a higher position in the electrochemical series displace a metal below it from its salt solution. The heat of displacement is the … Read more

The heat of precipitation is the energy change when one mole of precipitate is formed from its ion. Precipitation reaction occurs when two solutions containing cations and anions of insoluble salts added together. This reaction is known as the double decomposition reaction and is used to prepare any insoluble salt. The heat of precipitation is … Read more

Finding Heat of Reaction [begin{gathered}{text{Heat of Reaction, }}Delta {text{H}} hfill \{text{ = }}frac{{{text{Change of Energy}}}}{{{text{Number of Mole of Reactant/Product}}}} hfill \end{gathered} ] Q = mcθ m = mass of the substance that absorbs the heatc = specific heat capacity of the substance that absorbs the heatθ = change of temperature Notes: We always use the … Read more

Calculating Heat Change Heat change in a chemical reaction is directly proportional to the number of mole of reactant that takes part in a reaction or number of mole of product been produced. Example 1: N(g) + ½ O2(g) → NO2(g) ∆H = +66 kj mol-1 Calculate the heat change when 0.1 mole of nitrogen dioxide … Read more

The Heat of Reaction is the heat absorbed in a reaction at standard state condition between the numbers of moles of reactants shown in the equation for the reaction.  The Heat of reaction is represented by the symbol ∆H.  The unit of ∆H is kJmol-1.  If the reaction is exothernic, ∆H shows a value of … Read more

Relationship between Energy Change and Breaking/Formation of Bonds Breaking and Formation of Chemical Bond During a reaction, energy must be supplied to break bonds in the reactants, and energy is give out when the bonds in the products form. The amount of energy that absorbed or released depends on the strength of the bond. If … Read more

Energy Level Diagram When a chemical reaction occurs, certain amount of heat is given off or absorb. The energy change in the chemical reaction can be presented by an energy level diagram. An energy level diagram it is a graph that shows the energy change in a chemical reaction. Exothermic Reaction Figure below shows the … Read more