a) A combustion reaction is a chemical reaction in which a fuel, such as hydrogen, reacts with oxygen to produce heat, light, and other products.
b) The Gibbs energy equation is ∆G = ∆H - T∆S, where ∆G is the change in Gibbs free energy, ∆H is the change in enthalpy, T is the temperature in Kelvin, and ∆S is the change in entropy. This equation describes the spontaneity of a chemical reaction, where a negative ∆G indicates that the reaction is spontaneous and a positive ∆G indicates that the reaction is non-spontaneous.
∆G represents the maximum amount of non-expansion work that can be extracted from a thermodynamic system at constant temperature and pressure. A negative ∆G indicates that the reaction will proceed spontaneously, meaning that it will occur without the need for an external energy source. A positive ∆G indicates that the reaction is non-spontaneous, meaning that it will not occur without an external energy source.
c) The Gibbs energy for the combustion reaction of hydrogen and oxygen to form water is negative at 773 K, which means that the reaction is spontaneous under these conditions. This is because the negative ∆G value indicates that the reaction will release energy, and therefore the reaction will occur without the need for an external energy source. In other words, the products of the reaction (water) are at a lower energy state than the reactants (hydrogen and oxygen), which means that the reaction will proceed spontaneously in the direction of forming the products.