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3 years ago

What is the half-life of an isotope that decays to 6.25% of its original activity in 18.9 hours?

1 answer:

8 0

Radioactive material obeys 1st order decay kinetics,
For 1st order reaction, we have
k = $\frac{2.303}{t}Xlog \frac{\text{initial conc.}}{\text{final conc.}}$
where, k = rate constant of reaction

Given: Initial conc. 100, Final conc. = 6.25, t = 18.9 hours

∴ k = $\frac{2.303}{18.9} X log \frac{100}{6.25}$ = 0.1467 hours^(-1)

Now, for 1st order reactions: half life = $\frac{0.693}{k} = \frac{0.693}{0.1467}$ = 4.723 hours.

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A space probe on the surface of mars sends a radio signal back to earth,a distance of 7.19 ×10⁷ km. Radio travel at the speed of

lys-0071 [83]

Answer:

240 seconds

Explanation:

Data Given:

Distance Radio travel to earth = 7.19 ×10⁷ km

Speed of this radio signal = 3.00 ×10⁸ m/s

Solution:

First convert Km to m

1 km = 1000 m

7.19 ×10⁷ km = 7.19 ×10⁷ x 1000 = 7.19 × 10¹⁰m

Formula used to calculate time

Speed (S) = distance (d) / time (t)

rearrange above equation for time

time (t) = distance (d) / Speed (S) . . . . . . . . .(1)

Put values in equation 1

time (t) = 7.19 × 10¹⁰/ 3.00 ×10⁸ m/s

time (t) = 240 s

So 240 seconds it take for the signal to reach the earth

6 0

3 years ago

Click the "draw structure" button to launch the drawing utility. under certain reaction conditions, 2,3−dibromobutane reacts wit

REY [17]

Answer:

Explanation:

According to this. Let's analize the possible products a, b and c.

First, the problem states that we have 2 eq. of base, For this case, let's assume it's KOH. Now, As we are doing a reaction with base, means that this reaction can only take places under conditions of SN2 and E2, a fast reaction that is taking place in only 1 step.

With this in mind, let's analyze product a. This states that it has two sp hybridized carbon, in other words, a triple bond between two carbons. So the product is with no doubt, an alkyne.

Product b has only one sp hybridized carbon, which means that this carbon should cannot be an alkyne because we need two carbon atoms. The only way to have one atom of C sp hybridized, is with two double bonds, so product b would have to a alkene with two double bonds.

Product c do not have sp hybridized carbon, therefore, it only has two double bonds in two different Carbon atoms, so it's another alkene with two double bonds, but in two different atoms of carbon.

Picture attached show the product a, b and c. Hope this can help

4 0

3 years ago

A substance with a density of 2.70 g/mL occupies a volume of 21.3 mL. What is the mass of the sample? Report your answer in unit

katen-ka-za [31]

We know the formula of the density:
ρ = $\frac{m}{V}$ ;
So the mass will be equal to:
m = ρ * V = 2.70 * 21.3 = 57,51 g = 57510 mg of substance.
So the answer is 57510.

7 0

3 years ago

According to the National Institute of Health, ventricular tachycardia is a fast, regular beating of the ventricles that may las

jarptica [38.1K]

Answer:

1 makes the most sense

Explanation:

There is no way blood pressure will be decreased especially if your ventricles are erratically contracting for a long period of time. So 3 and 4 are out. And you said number 2 is wrong so my finally answer is 1.

3 0

3 years ago

What is the (a) frequency and (b) wavelength (in nm) of a source of purple light at the edge of the visible light spectrum?

stiv31 [10]

Answer: a) $Frequency=666\times10^{12}Hz-789\times10^{12}Hz$