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2 years ago

How many half-lives must elapse until 84 % of a radioactive sample of atoms has decayed? -g?

1 answer:

4 0

Half-life is the time required for decay of 50% of radio-active nuclei.

Thus, when radio-active material crosses 1st half-life, 100/2 = 50% radio-active material is left and remaining 50% is elapsed.

When, when radio-active material crosses 2nd half-life, 50/2 = 25% radio-active material is left and remaining 75% is elapsed.

When radio-active material crosses 3rd half-life, 25/2 = 12.5% radio-active material is left and remaining 87.5% is elapsed.

Thus, 2 <span>half-lives must elapse until 84 % of a radioactive sample of atoms has decayed.</span>

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READING CHECK

Wittaler [7]

Gas particles are in constant motion, and any object in motion has kinetic energy (Ek). ... For example, in the collision of two molecules, one molecule may be deflected at a slightly higher speed and the other at a slightly lower speed, but the average kinetic energy does not change.
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2 years ago

An ideal gas contained in a piston-cylinder assembly is compressed isothermally in an internally reversible process.

Tju [1.3M]

Answer:

a) $\Delta S$

b) entropy of the sistem equal to a), entropy of the universe grater than a).

Explanation:

a) The change of entropy for a reversible process:

$\delta S=\frac{\delta Q}{T}$

$\Delta S=\frac{Q}{T}$

The energy balance:

$\delta U=[tex]\delta Q- \delta W$

If the process is isothermical the U doesn't change:

$0=[tex]\delta Q- \delta W$

$\delta Q= \delta W$

$Q= W$

The work:

$W=\int_{V1}^{V2}P*dV$

If it is an ideal gas:

$P=\frac{n*R*T}{V}$

$W=\int_{V1}^{V2}\frac{n*R*T}{V}*dV$

Solving:

$W=n*R*T*ln(V2/V1)$

Replacing:

$\Delta S=\frac{n*R*T*ln(V2/V1)}{T}$

$\Delta S=n*R*ln(V2/V1)}$

Given that it's a compression: V2<V1 and ln(V2/V1)<0. So:

$\Delta S$

b) The entropy change of the sistem will be equal to the calculated in a), but the change of entropy of the universe will be 0 in a) (reversible process) and in b) has to be positive given that it is an irreversible process.

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3 years ago

Polyester is a synthetic material used for many different purposes. It is produced from petroleum and natural gas. Producing pol

notka56 [123]

Answer:

A. Producing certain synthetic materials could have a greater environmental impact than disposing of them.

Explanation

I just did this question and got it right.

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1 year ago

What is the graph of the orange line and is it a positive or negative connotation

dimulka [17.4K]

Answer:

Positive

Explanation:

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2 years ago

What temperature should vegetables be cooked at to hold them hot?

shtirl [24]

Answer:

135°F

Fruits and vegetables that are cooked for hot holding must be cooked to a temperature of 135°F (57.2 °C).

Explanation:

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2 years ago