Chemical reaction occurs when the chemical identity of the reactants is different from that of the products. A new substance forms with different properties from the original react Evidence that a chemical reaction has occurred can be a color change, light formation, gas bubbles formation, precipitate formation, or temperature change,
Use the following information to answer question 1.
QUESTION 1
Instant cold packs consist of ammonium nitrate and water. When the two are mixed, the temperature changes and becomes colder. It is described using the chemical equation
NH4NO3(s) → NH4+ (aq) + NO3(aq)
LA
Is this an example of an endothermic or exothermic reaction? Why?

Explanation:

Exothermic: the surrounds feel warmer. A wood fire stove is a good example of an exothermic reaction. You can feel the heat on your hands. It's exothermic.

Endothermic is exactly the opposite. The reaction takes place, but the heat comes from the surroundings. When you touch something that goes through an endothermic reaction, it feels much cooler.

This reaction, just by definition is endothermic.

part 1: the half-life of the element is 22 years.

part 2: it will take 132.02 year for the sample to decay from 308.0 g to 4.8125 g.

explanation:

part 1: there are two ways to determine the half life time.

first way: the half life time can be determined directly from its definition as it is the time required for the sample to decay to its half concentration.

from the data the initial concentration was 45.0 g and decayed to its half value (22.5 g) in 22.0 years.

second way: the radio active decay is considered first order reaction so we can use the laws of first order reactions.

k = (1/t) ln (a/a-x), where k is the rate constant of the reaction,

t is the time of the reaction

a is the initial concentration of the reactant

a-x is the remaining concentration at time (t)

a = 45.0 g the initial concentration at t = 0 year.

at t = 22 year, a-x = 22.5 g

then k = (1/22 year) ln (45.0 g/ 22.5 g) = 0.0315 year-1.

the half-life time (t1/2) = ln 2/ k = 0.693/ k =0.693/ 0.0315 = 22 years.

part 2:

using the same law k = (1/t) ln (a/a-x),

using the given data; a = 308.0 g and a-x = 4.8125 g and the calculated k from the part 1 (k = 0.0315 year-1)

t = (1/k) ln (a/a-x) = (1/0.0315) ln (308.0/ 4.8125) = 132.02 years