Enthalpy

• Neutralisation, combustion and condensation reactions are exothermic.
• In endothermic reactions, the products have a higher enthalpy than the reactants.
• Amount of heat gained or lost, q= mc△T
• enthalpy change, △H= -q/moles
• Joules --> kilojoules, divide by 1000
• kilojoules --> joules, multiply by 1000
• If there is a decrease in the temperature of the surrounding during a reaction process, then the reactions process is endothermic. Decrease in temperature means that the heat is being absorbed from the surroundings.
• Breaking of molecules into atoms is endothermic, Br2--> 2Br, since energy is absorbed.
• specific heat capacity of water= 4.18 J g^-1 K^-1
• the formation of black soot ( carbon, C) suggests that incomplete combustion occurred since there was an insufficient supply of O2 for the complete oxidation of the fuel.
• Combustion reaction= fuel + O2 --> CO2 + water
• Neutralisation reaction: acid + base--> salt + water
• Decomposition reaction is endothermic since energy is required for the breaking of bonds.
• negative enthalpy change, △H= exothermic
• positive enthalpy change, △H= endothermic
• Only conc. and temperature affect rate of reaction, not volume.
• In exothermic reaction, the products are more thermodynamically stable then the reactants.
• When conc. is increased, there is a faster rate of reaction, and this increase in rate of reaction leads to more rapid release in heat, thus, increasing the temperature.
• Bond breaking= endothermic and △H is positive
• Bond forming= exothermic and △H is negative
• methanol= CH3OH
• number of moles= grams used/ molar mass
• The standard enthalpy of formation of an element in its standard state is zero. Eg: O2, N2, H2 (both are gases).
• A reaction is exothermic if less energy is required to break the bonds in the reactants (weaker bonds) than is released when the bonds in products (stronger bonds) form.
• Combination of ion that will give greatest absolute lattice enthalpy: a small positive ion with a high charge and a small negative ion with a high charge.
• Ionization energy: it is the minimum energy required to remove one electron from the outermost shell of a gaseous ion.
• When the radius of the metal increases, the attraction between the ions decreases.
• most entropy, positive entropy, △S: gas
• least entropy, negative entropy, △S: solid
• increase in moles--> positive entropy
• A reaction is more likely or always spontaneous (-ve △G), if there is -ve △H and +ve △S.
• Spontaneous reaction: a reaction that proceeds without any external influence or any addition of energy at a given set of conditions.
• By Le Chatelier's principle, high pressure favours sides with lower moles of gas and vice versa (low pressure= more moles of gas)