# After two half-lives, how much of the original material has decayed? 25 percent 50 percent 75 percent 100 percent

75% of the material has decayed.

Explanation:

Hello,

We can start this problem by solving the first half-life assuming the arbitrary condition stating that the initial concentration has a value of 100M, thus, for the first half-life, the concentration dwindles to 50M. Afterwards, the second half-life yields a concentration of 25M, meaning that the 75% of the material has decayed up to the second half-life, of course, the half of the result from the first half-life.

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The correct answer to the question is 75 percent.

Let the original amount be 100%

From the question given above, the following data were:

Number of half-lives (n) = 2

Amount that has decayed =?

Next, we shall determine the amount remaining after 2 half-lives.

Original amount (N₀) = 100%

Amount remaining (N) =?

The amount remaining can be obtained as follow:

N = 25%

Finally, we shall determine the amount that has decayed.

Original amount (N₀) = 100%

Amount remaining (N) = 25%

Amount that has decayed =?

Amount that have decayed = (Original amount) – (Amount remaining)

Amount that have decayed = 100 – 25

Amount that have decayed = 75%

Thus, 75% of the original material has decayed.

## Related Questions

What happens to the temperature of the liquid in a cup of water as some of the water evaporates? A. The temperature increases because there are fewer molecules to share energy between.
B. The temperature decreases because new molecular bonds form.
C. The temperature decreases because the most energetic molecules escape.
D. The temperature increases because the vapor pressure increases.

Answer: C. The temperature decreases because the most energetic molecules escape.

Explanation: Evaporation is surface phenomenon in which liquid molecules gain energy from surrounding molecules and thus these high energy molecules escape from the surface in the form of vapors thus leaving low energy molecules in the system.

As the kinetic energy of the left molecules decreases, the temperature of the molecules decreases as kinetic energy is directly proportional to temperature. Thus low temperature results in cooling of the system.

R= gas constant

T= temperature

C. The temperature decreases because the most energetic molecules escape.

The normal boiling point of methanol is 64.7Â°c and the molar enthalpy of vaporization if 71.8 kj/mol. the value of Î´s when 2.15 mol of ch3oh (l) vaporizes at 64.7Â°c is __________ j/k.

The value or amount of heat that is needed in order to vaporize the given amount of methanol (CH3OH) can be calculated through the equation,
H = (n)(hf)

where H is the amount of heat
n is the given amount in mol, and
hf is the molar heat of vaporization

Substituting the known values,

H = (2.15 mol CH3OH)(71.8 kJ/mol)
H = 154.37 kJ

The molar enthalpy of vaporization is the amount of energy required to vaporize one mole of substance at a given temperature and pressure.

When we are given the amount of substance present, and the molar enthalpy of vaporization, we may simply use the formula:

ΔH = n * ΔH(vap)

To find the enthalpy change occurring

ΔH = 2.15 * 71.8

The value of ΔH is 154.27 kJ.

Which part of the atom is responsible for chemical bonding

It states the fact, which we now know, that electrons are responsible for the chemical bonding. According to this theory, valency is the number of electrons present in the outermost energy shell of the atom. This energy shell is called valency shell.

The two factors that determine whether a reaction is spontaneous or nonspontaneous are

The two factors that determine whether a reaction is spontaneous or nonspontaneous are entropy and energy. Let me know if this helps!

CH4 + 2O2 ? CO2 + 2H2O In the chemical reaction, if 10 moles of H2O are produced, moles of CO2 are also produced.

5 moles

Explanation:

This reaction (in the question) is a combustion reaction.

A combustion reaction is a reaction in which a substance (in this case an organic compound) is burnt in excess oxygen to produce carbon dioxide and water.

From the equation in the question, it can be deduced that the moles of the products are in the ratio 1:2 for CO₂ and H₂O respectively. Hence, when 10 moles of H₂O is produced, 5 moles of CO₂ will be produced.

1:2      (from the equation)

5:10   (for the answer)  ⇔ which is still the same as 1:2

5 moles. The H2O is getting multiplied by a factor 5. So therefore, the CO2 will have to be multiplied by 5 as well. 1x5=5.

What is the [OH-] in a solution with a poh of 3.90

Answer: The hydroxide ion concentration is

Explanation:

pOH is defined as the negative logarithm of hydroxide ion concentration in the solution.

To calculate the pOH of the reaction, we use the equation:

where,

Putting values in above equation, we get:

Hence, the hydroxide ion concentration is

Explanation:

A cubic box with sides of 20.0 cm contains 2.00 × 1023 molecules of helium with a root-mean-square speed (thermal speed) of 200 m/s. The mass of a helium molecule is 3.40 × 10-27 kg. What is the average pressure exerted by the molecules on the walls of the container? (The Boltzmann constant is 1.38 × 10-23 J/K and the ideal gas constant is R = 8.314 J/mol•K .) (12 pts.)

1.133 kPa is the average pressure exerted by the molecules on the walls of the container.

Explanation:

Side of the cubic box = s = 20.0 cm

Volume of the box ,V=

Root mean square speed of the of helium molecule : 200m/s

The formula used for root mean square speed is:

where,

= root mean square speed

k = Boltzmann’s constant =

T = temperature = 370 K

M = mass helium =

Moles of helium gas = n

Number of helium molecules = N =

N =

Ideal gas equation:

PV = nRT

Substitution of values of T and n from above :

(1 Pa = 0.001 kPa)

1.133 kPa is the average pressure exerted by the molecules on the walls of the container.

The f sublevel has___ orbitals.