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AnnZ [28]
3 years ago
5

Fluorine-21 has a half life of approximately 5 seconds. You have 340 grams, what fraction of the original nuclei would remain af

ter 20 seconds?
Chemistry
1 answer:
madreJ [45]3 years ago
7 0
The half life equation is -->P(t) = Pi (0.5) ^ (t/c)
c is equal to the element to reach its half-life (5 seconds)t is equal to the duration of time the element is expose to (20 seconds)Pi is the initial amount (340)0.5 is the base of this exponential function to represent half-life.P(t) is the expression for the function of time

P(20) = 340 (0.5)^20/5P(20) = 340 (0.5) ^4P(20)= 21.25 grams
Fraction = P(t)/Pi              = P(20)/Pi              =21.25/340              =1/16
Therefore, when given 20 seconds, 340 grams of Fluorine-21 will degrade to 21.25 grams OR 1/16 of its original mass.
Hope this method helps! (This is my answer btw, I think you may have accidentally posted twice?)
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Consider the dissolution of calcium hydroxide:
Crazy boy [7]

Answer:

1. K_eq = [Ca^{2+][OH^-]^2 = K_{sp}

2. a. No effect;

b. Products;

c. Products;

d. Reactants

Explanation:

1. Equilibrium constant might be written using standard guidelines:

  • only aqueous species and gases are included in the equilibrium constant excluding solids and liquids;
  • the constant involves two parts: in the numerator of a fraction we include the product of the concentrations of products;
  • the denominator includes the product of the concentrations of reactants;
  • the concentrations are raised to the power of the coefficients in the balanced chemical equation.

Based on the guidelines, we have two ions on the product side, a solid on the left side. Thus, the equilibrium constant has the following expression:

K_eq = [Ca^{2+][OH^-]^2 = K_{sp}

2. a. In the following problems, we'll be considering the common ion effect. According to the principle of Le Chatelier, an increase in concentration of any of the ions would shift the equilibrium towards the formation of our precipitate.

In this problem, we're adding calcium carbonate. It is insoluble, so it wouldn't have any effect on the equilibrium.

b. Sodium carbonate is completely soluble, it would release carbonate ions. The carbonate ions would combine with calcium cations and more precipitate would dissolve. This would shift the equilibrium towards formation of the products to reproduce the amount of calcium cations.                                      

c. HCl would neutralize calcium hydroxide to produce calcium chloride and water, so the amount of calcium ions would increase, therefore, the products are favored.

d. NaOH contains hydroxide anions, so we'd have a common ion. An increase in hydroxide would produce more precipitate, so our reactants are favored.

3 0
3 years ago
You are experimenting to find out if fertilizer makes a plant grow taller. What would be an appropriate control group for this e
leonid [27]

Answer:

If plants are given nitrogen fertilizer, then they will grow taller. ... Factors in an experiment that a scientist PURPOSELY Changes (manipulated) Control Group ... to test various amounts of fertilizer to find out what amount makes plants grow

Explanation:

3 0
3 years ago
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6 0
3 years ago
Read 2 more answers
Limiting Reactant Worksheet
faltersainse [42]

Answer:

a) 1.61 mol

b) Al is limiting reactant

c) HBr is in excess

Explanation:

Given data:

Moles of Al = 3.22 mol

Moles of HBr = 4.96 mol

Moles of H₂ formed = ?

What is limiting reactant =

What is excess reactant = ?

Solution:

Chemical equation:

2Al  + 2HBr  → 2AlBr + H₂

Now we will compare the moles:

                Al              :               H₂

                  2              :               1

                 3.22         :            1/2×3.22 = 1.61 mol

                HBr            :              H₂

                 2                :               1

                4.96            :          1/2×4.96 = 2.48 mol      

The number of moles of H₂ produced by Al are less it will be limiting reactant while HBr is present in excess.

Moles of H₂ :

Number of moles of H₂ = 1.61 mol

6 0
3 years ago
Chemical reactions that ____ energy will not occur without a source of energy
andrezito [222]
Chemical reactions that release energy will not occur without a source of energy.  So the answer is release.
4 0
3 years ago
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