ka

Ka is a term with several distinct meanings across different fields, including religion, science, and chronology. In encyclopedic contexts it is treated as a disambiguation term for these varied senses.

In ancient Egyptian religion, ka denotes a person’s life force or spiritual double. It was believed to accompany the living person from birth and to persist after death, inhabiting the tomb, statue, or imagery of the deceased. The ka required nourishment in offerings, and tombs often contained food, models, or inscriptions to sustain it. The concept is commonly discussed alongside the ba, another aspect of the soul, and with the later akh. Rituals such as the opening of the mouth were performed to enable the deceased to receive offerings and to sustain the ka in the afterlife.

In chemistry, Ka denotes the acid dissociation constant, a measure of the strength of an acid in solution. For the equilibrium HA ⇌ H+ + A−, Ka = [H+][A−]/[HA]. Smaller Ka values indicate weaker acids. The negative logarithm, pKa = −log10 Ka, is frequently used to compare acid strengths and to calculate pH and buffer behavior. Ka values depend on temperature and solvent and are a key parameter in quantitative acid–base chemistry.

In geology and archaeology, ka stands for kiloannum, a unit equal to 1,000 years. It is used to express dates and durations, often in radiometric dating and stratigraphic contexts. For example, 65 ka means 65,000 years ago. The term is commonly encountered in discussions of deep time and prehistoric chronology.