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shtirl [24]
3 years ago
13

A particular element found in nature exists as two stable isotopes. 60.4% of the element has a mass of 68.9257amu, the rest of t

he element is found with a mass of 70.9249 amu. Calculate the average atomic mass of the element.
Chemistry
1 answer:
miss Akunina [59]3 years ago
6 0
Mass           %abundance        # of atoms (pick 1000 sample)
68.9257         60.4%                  604
70.9249         39.6%                  396
*39.6* ( i got this by subtracting 100 as most percentage is out of 100)
*# of atoms* ( i just moved it one decimal place, then i am going to make the sample out of 1000, to get the decimal place)

Formula= total mass/ total #atoms

x= (68.9257u* 604) + (70. 9249*396)/ 1000
x- 69717. 3832/ 1000
x= 69.717amu or 69.72 amu 

if you look on the periodic table the closet element with that mass is gallium ( amu is 69.72)
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4 years ago
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In a coffee cup calorimeter, 1.60 g of NH4NO3 is mixed with 75.0 g of water at an initial temperature of 25.00 degrees C. After
igomit [66]

Answer:

+26.6kJ/mol

Explanation:

The enthalpy of dissolution of NH₄NO₃ is:

NH₄NO₃(aq) + ΔH  → NH₄⁺ + NO₃⁻

Where ΔH is the heat of reaction that is absorbed per mole of NH₄NO₃,

The moles that reacts in 1.60g are (Molar mass NH₄NO₃:80g/mol):

1.60g * * (1mol / 80g) = 0.02 moles reacts

To find the heat released in the coffee cup calorimeter, we must use the equation:

Q = m×ΔT×C

Where Q is heat released,

m is mass of the solution

ΔT is change in temperature (Final temperature - Initial temperature)

C is specific heat of the solution (4.18J/g°C)

Mass of the solution is:

1.60g + 75g = 76.60g

Change in temperature is:

25.00°C - 23.34°C = 1.66°C

Replacing:

Q = m×ΔT×C

Q = 76.60g×1.66°C×4.18J/g°C

Q = 531.5J

This is the heat released per 0.02mol. The heat released per mole (Enthalpy change for the dissolution of NH₄NO₃) is:

531.5J / 0.02mol = 26576J/ mol =

+26.6kJ/mol

<em>+ because the heat is absorbed, the reaction is endothermic-</em>

7 0
3 years ago
** ANSWER FAST I WILL MARK YOU BRAINLIEST AND GIVE 20 POINTS * * THIS IS A CHEMISTRY QUESTION SO PLEASE ONLY ANSWER IF YOU ARE G
Anna11 [10]

Answer:

\boxed{\text{ B. Increase the temperature and decrease the pressure.}}

Explanation:

Let's say the reaction is

R ⇌ 2P; endothermic

I like to consider heat as if it were a reactant or a product in a chemical equilibrium.

Another way to write the equilibrium would be

heat + R ⇌ 2P

According to Le Châtelier's Principle, when a stress is applied to a system at equilibrium, the system will respond in a way that tends to relieve the stress.

Let's consider each of the stresses in turn.

(i) Changing the temperature

If you want to increase the amount of product, you increase the temperature. The system will try to get rid of the added heat by shifting to the right, thus forming more product.

(ii) Changing the pressure

If R and P are liquids or solids or in aqueous solution, changing the pressure will have no effect. Something must be in the gas phase for a change in pressure to affect the position of equilibrium.

If P is a gas, the equilibrium is

heat + R ⇌ 2P(g)

Then, decreasing the pressure will produce more P. If you reduce the pressure, the system will respond by shifting to the right (the side with more gas molecules) to produce more P and bring the pressure back up

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4 years ago
In the scientific method, analysis should follow right after
alina1380 [7]
Observation/ question
research
hypothesis
<span>experiment
</span>analysis
conclusion
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3 years ago
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