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Anon25 [30]
3 years ago
13

The energy required to dissociate KF into neutral atoms is 498 kJ/mol. Given that the first ionization energy for K is 418 kJ/mo

l, calculate the electron affinity (in kJ/mol) for F. Show your work for all calculations.
Physics
1 answer:
mojhsa [17]3 years ago
7 0

Answer: Electron affinity of F equals

275.8kJ/mol

Explanation: Electron affinity is the energy change when an atom gains an electron.

Let's first calculate the energy required -E(r)to dissociate KF into ions not neutral atom which is given.

E(r) = {z1*z2*e²}/{4π*permitivity of space*r}

z1 is -1 for flourine

z2 is +1 for potassium

e is magnitude of charge 1.602*EXP{-9}C

r is ionic bond length of KF(is a constant for KF 0.217nm)

permitivity of free space 8.854*EXP{-12}.

Now let's solve

E(r)= {(-1)*(1)*(1.602*EXP{-9})²} /

{4*3.142*8.854*EXP(-12)*0.217*EXP(-9)

E(r) = - 1.063*EXP{-18}J

But the energy is released out that is exothermic so we find - E(r)

Which is +1.603*EXP{-18}J

Let's now convert this into kJ/mol

By multiplying by Avogadro constant 6.022*EXP(23) for the mole and diving by 1000 for the kilo

So we have,

1.603*EXP(-18) *6.022*EXP(23)/1000

-E(r) = 640.2kJ/mol.

Now let's obtain our electron affinity for F

We use this equation

Energy of dissociation (nuetral atom)= electron affinity of F +(-E(r)) + ionization energy of K.

498kJ/mol

=e affinity of F + 640.2kJ/mol

+(-418kJ/mol)

(Notice the negative sign in ionization energy for K. since it ionize by losing an electron)

Making electron affinity of F subject of formula we have

Electron affinity (F)=498+418-640.2

=275.8kJ/mol.

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A 125 W motor accelerates a block along a level, frictionless surface at an average speed of 5.0
Lelu [443]

Answer:

25N

Explanation:

Given parameters:

Power of the motor = 125W

Average speed  = 5m/s

Unknown:

Force supplied to the motor = ?

Solution:

 Work done is the force applied to move a body through a particular distance;

         Work done  = Force x distance

Also,

        Work done  = Power x time

 

So;

             Force x distance = Power  x time

  since force is the unknown;

            Force  = \frac{Power x time}{distance}

         Speed  = \frac{distance }{time}

             Force  = \frac{Power}{speed}

Now solve;

                Force  = \frac{125}{5}    = 25N

3 0
3 years ago
Explain why convex mirrors can only produce virtual images. Please use at least 2 content related sentences. (ref: p.471-481)
34kurt

Convex mirrors can only produce virtual images because the focal point and the center of curvature of the convex mirror are imaginary points and that cannot be reached.

<h3>What is virtual image?</h3>

This is referred to the opposite of a real image and cannot be obtained on a screen. It is formed from the  apparent divergent of light rays from a point  and not the actual one which is the major difference it has with a real image.

It is usually produced by a convex mirror because the focal point and the center of curvature of the convex mirror are imaginary points which can't be reached.

Read more about Convex mirrors here brainly.com/question/14269744

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8 0
2 years ago
A 2.85 kg fish is attached to the lower end of a vertical spring that has negligible mass and force constant 875 N/m. The spring
Westkost [7]

Answer:

A) V = 0.324 m/s

B) V = 0.56 m/s

Explanation:

A) Change in gravitational potential energy = mass * gravity * height change

Change in G.P.E = 2.85 * 9.81 * 0.058 = 1.6215 J

Energy transferred to spring = 0.5 * k * x^2

Here k = 875 N/m

And x = 0.058 m

Thus energy transferred to spring = 1.47175 J

The G.P.E is converted to spring potential energy and kinetic energy as it moves down. So the difference in energy is accounted by kinetic energy as follows:

Kinetic energy = G.P.E - Spring P.E

Kinetic energy = 1.6215 - 1.47175 = 0.14975 J

We can now find the speed using this kinetic energy:

Kinetic energy = 0.14975

0.5 * mass * velocity^2 = 0.14975

0.5 * 2.85 * V^2 = 0.14975

V = 0.324 m/s

B) The fish accelerates because the force on it are unbalanced. These forces are the weight of the fish, and the force of the spring stopping it.

As long as the weight of the fish is more than the upward force of the spring, the fish will continue to accelerate. Using this knowledge, we can deduce that the speed is maximum when the weight and spring force are equal. Thus we set them equal and find out the displacement first:

Weight = spring force

2.85 * 9.81 = 875 * Displacement

Displacement = 0.03195 m

Similarly as (A):

Change in G.P.E = 2.85 * 9.81 * 0.03195 = 0.8933 J

Spring P.E = 0.5 * 875 * 0.03195^2 = 0.4466 J

Kinetic energy = 0.8933 - 0.4466 = 0.4467 J

0.5 * mass * V^2 = 0.4467

0.5 * 2.85 * V^2 = 0.4467

V = 0.56 m/s

4 0
3 years ago
At high speeds, a particular automobile is capable of an acceleration of about 0.540 m/s^2. At this rate, how long (in seconds)
Mama L [17]

Answer:

t = 6.68 seconds

Explanation:

The acceleration of the automobile, a=0.54\ m/s^2

Initial speed of the automobile, u = 91 km/hr = 25.27 m/s

Final speed of the automobile, v = 104 km/hr = 28.88 m/s

Let t is the time taken to accelerate from u to v. It can be calculated as the following formula as :

t=\dfrac{v-u}{a}

t=\dfrac{28.88-25.27}{0.54}

t = 6.68 seconds

So, the time taken by the automobile to accelerate from u to v is 6.68 seconds. Hence, this is the required solution.

5 0
3 years ago
The ball of a ballpoint pen is 0.5 mm in diameter and has an ASTM grain size of 12. How many grainsare there in the ball
Alina [70]

Answer:

the number of grains in the ball is 274,848

Explanation:

Given that;

diameter = 0.5 mm

so radius r = 0.25 mm

first we determine the volume of the ball using the following equation;

V = 4/3×πr³

we substitute

V = 4/3×π(0.25)³

V =  0.06544 mm³

Now form table 1.1 "Grain sizes" a metal with grain size number of 12 has about 4,200,000 grains/mm³

so;

Number of grains N = 0.06544 × 4,200,000

N = 274,848 grains

Therefore, the number of grains in the ball is 274,848

5 0
2 years ago
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