Acids and Alkalis: Energy Changes and Reactions

Acids and alkalis can react chemically together, producing a liquid called salt and water. This process is referred to as neutralisation.
Acids have a sour taste and can turn litmus paper red, while alkalis are typically bitter and turn litmus paper blue.
In energy terms, all chemical reactions including those between acids and alkalis can be either exothermic or endothermic. Exothermic reactions release heat into the environment while endothermic reactions absorb heat.
The pH scale measures how acidic or basic a substance is, ranging from 0 (very acidic) to 14 (very basic). A pH of 7 is neutral, for pure water.
Indicators such as litmus paper, universal indicator or phenolphthalein can be used to measure the pH of a solution. Different indicators change colour at different pH values.
A reaction between an acid and metal will typically produce a salt and hydrogen gas. The more reactive the metal, the more vigorous the reaction.
A reaction between an acid and a base will produce a salt and water. This is called a neutralisation reaction. In this case, the base can be an alkali, metal oxide or metal hydroxide.
The law of conservation of energy states that energy cannot be created or destroyed, only transferred from one form to another. In chemical reactions, this could be from potential energy in the bonds of the reactants to kinetic energy in the products.
Different reactions involve different energy changes, which can be measured using a thermometer. A temperature decrease indicates an endothermic reaction while a temperature increase indicates an exothermic reaction.
Energy profile diagrams can be used to visually represent the energy changes during a chemical reaction. The difference in energy between the reactants and products represents the overall energy change.
The activation energy (EA) is the minimum amount of energy required for a reaction to occur. Catalysts can be used to lower the activation energy of a reaction and increase the reaction rate.
In a reversible reaction, the products can react to form the original reactants. These reactions can reach a dynamic equilibrium where the forward and reverse reactions occur at the same rate. The position of equilibrium can be affected by changes in temperature or pressure.