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2 years ago

A radioactive isotope has a half-life of 2.5 years. Which fraction of the original mass remains unchanged after 10 years?

Chemistry

2 answers:

kodGreya [7K]2 years ago

8 0

Answer is: 1/16 of the original mass remains unchanged after 10 years

Take 100 atoms:

After first half-life (2.5 years): 50% · 100 ÷ 100% = 50 or 1/2.

After second half-life (5 years): 0.5 · 50 = 25 or 1/4.

After third half-life (7.5 years): 0.5 · 25 = 12.5 or 1/8.

After fourth half-life (10 years): 0.5 · 12.5 = 6.25 or 1/16.

6.25 ÷ 100 · 100% = 6.25% or 1/16.

Salsk061 [2.6K]2 years ago

5 0

Using the following equation.

A = Ao (1/2) ^n 
n = 4 
A = Ao (1/2)^4
= 1/16

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An amount of solid barium chloride, 20.8 g, is dissolved in 100 g water in a coffee-cup calorimeter by the reaction: BaCl2 (s) 

mamaluj [8]

Answer : The enthalpy change during the reaction is -6.48 kJ/mole

Explanation :

First we have to calculate the heat gained by the reaction.

$q=m\times c\times (T_{final}-T_{initial})$

where,

q = heat gained = ?

m = mass of water = 100 g

c = specific heat = $4.04J/g^oC$

$T_{final}$ = final temperature = $26.6^oC$

$T_{initial}$ = initial temperature = $25.0^oC$

Now put all the given values in the above formula, we get:

$q=100g\times 4.04J/g^oC\times (26.6-25.0)^oC$

$q=646.4J$

Now we have to calculate the enthalpy change during the reaction.

$\Delta H=-\frac{q}{n}$

where,

$\Delta H$ = enthalpy change = ?

q = heat gained = 23.4 kJ

n = number of moles barium chloride = $\frac{\text{Mass of barium chloride}}{\text{Molar mass of barium chloride}}=\frac{20.8g}{208.23g/mol}=0.0998mole$

$\Delta H=-\frac{646.4J}{0.0998mole}=-6476.95J/mole=-6.48kJ/mole$

Therefore, the enthalpy change during the reaction is -6.48 kJ/mole

8 0

2 years ago

What are the answers to these questions

Virty [35]

Answer:

Explanation:

So basically it just asking you question about that surtain subject .

5 0

2 years ago

When the reaction CO2(g) + H2(g) ⇄ H2O(g) + CO(g) is at equilibrium at 1800◦C, the equilibrium concentrations are found to be [C

UNO [17]

Answer:

The new molar concentration of CO at equilibrium will be :[CO]=1.16 M.

Explanation:

Equilibrium concentration of all reactant and product:

$[CO_2] = 0.24 M, [H_2] = 0.24 M, [H_2O] = 0.48 M, [CO] = 0.48 M$

Equilibrium constant of the reaction :

$K=\frac{[H_2O][CO]}{[CO_2][H_2]}=\frac{0.48 M\times 0.48 M}{0.24 M\times 0.24 M}$

K = 4

$CO_2(g) + H_2(g) \rightleftharpoons H_2O(g) + CO(g)$

Concentration at eq'm:

0.24 M 0.24 M 0.48 M 0.48 M

After addition of 0.34 moles per liter of $CO_2$ and $H_2$ are added.

(0.24+0.34) M (0.24+0.34) M (0.48+x)M (0.48+x)M

Equilibrium constant of the reaction after addition of more carbon dioxide and water:

$K=4=\frac{(0.48+x)M\times (0.48+x)M}{(0.24+0.34)\times (0.24+0.34) M}$

$4=\frac{(0.48+x)^2}{(0.24+0.34)^2}$

Solving for x: x = 0.68

The new molar concentration of CO at equilibrium will be:

[CO]= (0.48+x)M = (0.48+0.68 )M = 1.16 M

3 0

2 years ago

Which of the following compounds would be most effective in lowering the melting point of ice on roads? a) CaCl2 b) NaCl C) K3PO

Mrac [35]

I'm not 100% sure on this, but I would go with C) NaCl.
NaCl is a salt, and that is used to melt the ice on the roads. Hope this helps!

7 0

2 years ago

A turtle moves at a speed of 1.0km/h. How fast is the turtle moving in meter per second (m/s)?

ahrayia [7]

Answer:

0.28m/s

Explanation:

Speed is defined as the distance travelled per unit of time. The speed of the turtle is 1.0km/h. Thus, to find the speed in m/s, we need to convert km to m (1km is 1000m), and h to s (1h = 3600s).

Converting units:

1.0km/h * (1000m / 1km) * (1h / 3600s) = 0.28m/s.

The speed of the turtle in meter per second is 0.28m/s

7 0

2 years ago