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Allisa [31]
4 years ago
13

Element X had a mass of 300g and a 1/2 life of 10 years. how many grams will remain after 40 years?

Chemistry
1 answer:
kiruha [24]4 years ago
3 0
<h3>Answer:</h3>

18.75 grams

<h3>Explanation:</h3>
  • Half-life refers to the time taken by a radioactive material to decay by half of the original mass.
  • In this case, the half-life of element X is 10 years, which means it takes 10 years for a given mass of the element to decay by half of its original mass.
  • To calculate the amount that remained after decay we use;

Remaining mass = Original mass × (1/2)^n, where n is the number of half-lives

Number of half-lives = Time for the decay ÷ Half-life

                                 = 40 years ÷ 10 years

                                  = 4

Therefore;

Remaining mass = 300 g × (1/2)⁴

                            = 300 g × 1/16

                             = 18.75 g

Hence, a mass of 300 g of an element X decays to 18.75 g after 40 years.

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3 0
3 years ago
A sample of liquid heptane (C7H16) weighing 11.5 g is reacted with 1.3 mol of oxygen gas. The heptane is burned completely (hept
Anna11 [10]

Answer:

a) 0.525 mol

b) 0.525 mol

c) 0.236 mol

Explanation:

The combustion reactions (partial and total) will be:

C₇H₁₆ + (15/2)O₂ → 7CO + 8H₂O

C₇H₁₆ + 11O₂ → 7CO₂ + 8H₂O

---------------------------------------------------

2C₇H₁₆ + (37/2)O₂ → 7CO + 7CO₂ + 16H₂O

It means that the reaction will form 50% of each gas.

a) 0.525 mol of CO

b) 0.525 mol of CO₂

c) The molar mass of heptane is: 7*12 g/mol of C + 16*1 g/mol of H = 100 g/mol

So, the number of moles is the mass divided by the molar mass:

n = 11.5/100 = 0.115 mol

For the stoichiometry:

2 mol of C₇H₁₆ -------------- (37/2) mol of O₂

0.115 mol of C₇H₁₆ --------- x

By a simple direct three rule:

2x = 2.1275

x = 1.064 mol of O₂

Which is the moles of oxygen that reacts, so are leftover:

1.3 - 1.064 = 0.236 mol of O₂

5 0
4 years ago
An initial mixture of nitrogen gas and hydrogen gas is reacted in a rigid container at a certain temperature as follows: 3 H2(g)
Luden [163]

Answer:

[H₂] = 13 M

[N₂] = 12 M

Explanation:

Let´s consider the following reaction at equilibrium.

3 H₂(g) + N₂(g) ⇄ 2 NH₃(g)

To find out the initial concentrations we will use an ICE chart. We recognize 3 stages: Initial, Change and Equilibrium and complete each row with the concentration or change in concentration. We will use letters for the unknown data.

          3 H₂(g) + N₂(g) ⇄ 2 NH₃(g)

I              a           b                0

C          -3x         -x              +2x

E         a - 3x     b - x             2x

We know that,

[NH₃] = 2x = 5.1 M ⇒ x = 2.6 M

Then,

[H₂] = 5.6 M = a - 3x ⇒ a = 13 M

[N₂] = 9.3 M = b - x ⇒ b = 12 M

7 0
4 years ago
Calculate % oxygen in CO (NO)3
Alexxx [7]

50 percent

there are 8 atoms in this molecule

and 4 of them are oxygen molc. so:

\frac{4}{8}  \times 100 = \%50

good luck

8 0
3 years ago
The diagram shows changes of state between solid, liquid, and gas. The atoms of a substance lose energy during a change of state
Julli [10]

Answer:

yes it L

Explanation:

5 0
3 years ago
Read 2 more answers
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