A wooden artifact from a Chinese temple has a 14C activity of 42.8 counts per minute as compared with an activity of 58.2 counts per minute for a standard of zero age. Part A From the half-life for 14C decay, 5715 yr, determine the age of the artifact.

Answer : The age of the artifact is,

Explanation :

Half-life = 5715 years

First we have to calculate the rate constant, we use the formula :

Now we have to calculate the time taken to decay.

Expression for rate law for first order kinetics is given by:

where,

k = rate constant

t = time taken by sample = ?

a = initial activity of the reactant  = 58.2 counts per minute

a - x = activity left after decay process  = 42.8 counts per minute

Now put all the given values in above equation, we get

Therefore, the age of the artifact is,

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.