Radioactive elements decay via first-order kinetics. consider a certain type of nucleus that has a rate constant of 2.4 × 10–2 h–1. a sample contains 6.5 × 108 radioactive nuclides. calculate the time required for 59% of the nuclides to decompose.

37.15 h.

Explanation:

where, k is the rate constant of the reaction (k = 2.4 x 10⁻² h⁻¹).

t is the time of the reaction (t = ??? day).

a is the initial concentration of nuclides (a = 100 %).

(a-x) is the remaining concentration of nuclides (a - x = 100% - 59% = 41.0 %).

∴ kt = lna/(a-x)

(2.4 x 10⁻² h⁻¹)(t) = ln(100.0%)/(41.0%).

(2.4 x 10⁻² h⁻¹)(t) = 0.8916.

∴ t = (0.8916)/(2.4 x 10⁻² h⁻¹) = 37.15 h.

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.