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Eddi Din [679]
3 years ago
9

A radioactive substance of mass 768g has a half life of 3 years. After how many years does it leave only 6g undecayed?​

Chemistry
2 answers:
vagabundo [1.1K]3 years ago
8 0

Answer:

The answer is 21 years.

Explanation:

7×3

sammy [17]3 years ago
5 0

Answer:

hi

good morning

myself veeresh

and you

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A square table has an area of 400 square feet. They want to cut the table into two equal rectangles. If they cut the table in ha
Orlov [11]

Answer:

b=200

l=100

Explanation:

so since it is a square all sides would be equal

when you cut the square vertically the dimensions will change

the bredth would be same that is 200

but the length would be half that is 100

7 0
3 years ago
There are many ways that you can tell whether a chemical change has occurred. Which of the following is NOT a sign of chemical c
Vesnalui [34]

Answer:

liquid bolling

Explanation:

because it just using heat.

7 0
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Read 2 more answers
How many moles are in 64.8 l of f2 gas
Licemer1 [7]
6.02×[10]1 ×64.8=3900.96 moles
7 0
2 years ago
Determine the heat of reaction (ΔHrxn) for the combustion of ethanol (C2H5OH) by using heat of formation data: C2H5OH (l) + 3 O2
egoroff_w [7]

Answer:

\Delta H_{rxn}=-1234.782kJ

Explanation:

\Delta H_{rxn}=\sum [n_{i}\times \Delta H_{f}^{0}(product)_{i}]-\sum [n_{j}\times \Delta H_{f}^{0}(reactant_{j})]

Where n_{i} and n_{j} are number of moles of product and reactant respectively (equal to their stoichiometric coefficient).

\Delta H_{f}^{0} is standard heat of formation.

So, \Delta H_{rxn}=[2mol\times \Delta H_{f}^{0}(CO_{2})_{g}]+[3mol\times \Delta H_{f}^{0}(H_{2}O)_{g}]-[1mol\times \Delta H_{f}^{0}(C_{2}H_{5}OH)_{l}]-[3mol\times \Delta H_{f}^{0}(O_{2})_{g}]

or, \Delta H_{rxn}=[2mol\times -393.509kJ/mol]+[3mol\times -241.818kJ/mol]-[1mol\times -277.69kJ/mol]-[3mol\times 0kJ/mol]

or, \Delta H_{rxn}=-1234.782kJ

4 0
3 years ago
What is the molar solubility of marble (i.e., [ca2 ] in a saturated solution in normal rainwater, for which ph=5.60? express you
Brut [27]
Missing in your question :

Ksp of(CaCO3)= 4.5 x 10 -9

Ka1 for (H2CO3) =  4.7 x 10^-7

Ka2 for (H2CO3) = 5.6 x 10 ^-11

1) equation 1 for Ksp = 4.5 x 10^-9 

CaCO3(s)→ Ca +2(aq)    +  CO3-2(aq)  

2) equation 2 for Ka1 = 4.7 x 10^-7

 H2CO3 + H2O → HCO3- + H3O+

3) equation 3 for Ka2 = 5.6 x 10^-11

 HCO3-(aq) + H2O(l) → CO3-2 (aq)  + H3O+(aq)

so, form equation 1& 2&3 we can get the overall equation:
CaCO3(s)  +  H+(aq)  → Ca2+(aq)   + HCO3-(aq)

note: you could get the overall equation by adding equation 1 to the inverse of equation 3 as the following:
when the inverse of equation 3 is :

CO3-2 (aq) + H3O+ (aq) ↔ HCO3- (aq) + H2O(l)  Ka2^-1 = 1.79 x 10^10
when we add it to equation 1
CaCO3(s) ↔ Ca2+(aq)  +  CO3-2(aq)   Ksp = 4.5 x 10^-9

∴ the overall equation will be as we have mentioned before:
when H3O+ = H+

CaCO3(s) + H+(aq)  ↔ Ca2+ (aq) + HCO3-(aq)   K= 80.55

from the overall equation:

∴K = [Ca2+][HCO3-] / [H+]

when we have [Ca2+] = [HCO3-] so we can assume both = X

∴K = X^2 / [H+]

when we have the PH = 5.6 so we can get [H+]

PH = - ㏒[H+]
5.6 = -㏒[H]
∴[H] = 2.5 x 10^-6

so, by substitution on K expression:

∴ 80.55 = X^2 / (2.5 x10^-6)

∴X = 0.0142

∴[Ca2+] = X = 0.0142 
6 0
3 years ago
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