Please help ASAP and please don’t put random stuff for points I actually need help so please

How many valence electrons does an atom of rubidium (Rb atomic number 37) have? A.One B.Five C.Six D.37

nadezda [96]

Electronic configuration of Rb: 2.8.8.8.8.3
Valence electron is 3....

4 0

3 years ago

When a 12.8 g sample of KCL dissolves in 75.0 g of water in a calorimeter the temp. drops from 31 Celsius to 21.6 Celsius. Calcu

Delicious77 [7]

Answer:

Step 1: Calculate qsur (the surrounding is

usually the water)

qsur = ? J

m = 75.0 g water

c = 4.184 J/g

oC

ΔT = (Tfinal- Tinitial)= (21.6 – 31.0) = -9.4 oC

qsur = m · c · (ΔT)

qsur = (75.0g) (4.184 J/g

oC) (-9.4 oC)

qsur = - 2949.72 J

First, using the information we know that we

must solve for qsur, which is the water. We know

the mass for water, 75.0g, the specific heat of

the water, 4.184 j/g

o

c, and the change in

temperature, 21.6-31.0 = -9.4 oC. Plugging it

into the equation, we solve for qsur.

Step 2: Calculate qsys qsys = - (qsur)

qsys = - (- 2949.72 J)

qsys = + 2949.72

In this case, the qsur is negative, which means

that the water lost energy. Where did it go? It

went to the system. Thus, the energy of the

system is negative, opposite, the energy of the

surrounding.

Step 3: Calculate moles of the substance

that is the system

Given: 12.8 g KCl

Mol system = (g system given)

(molar mass of system)

Mol system = (12.8 g KCl)

(39.10g + 35.45g)

Mol system = 12.8 g KCl

74.55 g

Mol system = 0.172

Here, we solve for the mol in the system by

using the molar mass of the material in the

system.

Step 4: Calculate ΔH ΔH = q sys .

Mol system

ΔH= + 2949.72 J

0.172 mol

ΔH= +17179.81 J/mol or +1.72 x 104

J/mol

i hope this helps

7 0

3 years ago

What is the energy of a photon of infrared radiation with a frequency of 2.53 × 1012 Hz? Planck’s constant is

Novosadov [1.4K]

It is letter b or c nit d

6 0

1 year ago

a certain piece of copper wire is determined to have a mass of 2.0 0g per meter how many centimeters of the wire would be needed

harina [27]

The given question tells you that a certain piece of wire has a mass = 2.0 g per meter

That means that if you consider a piece of wire that is 1 m in length, its mass will be equal to 2.00 g .

According to question,

Now, you know that

1 m = 100 cm

Mass of 2.00 g of copper will correspond to a wire that is a 100 cm long.

This implies that 0.28 gof copper will correspond to a wire that is

0.28 g * 100 cm / 2.0 g = 14 cm long

Hence, 14 cm of the wire would be needed to provide 0.28 g of copper.

Properties of Copper :

High conductivity and ductility.

Non magnetic.

To know more about Copper here:

brainly.com/question/19761029?referrer=searchResults

#SPJ4

3 0

1 year ago

A mixture of ethyl acetate vapour and air has a relative saturation of 50% at 303 K and a total pressure of 100 kPa. If the vapo

AURORKA [14]

Answer : The correct option is, (b) 0.087

Explanation :

The formula used for relative saturation is:

$\text{Relative saturation}=\frac{P_A}{P_A^o}$

where,

$P_A$ = partial pressure of ethyl acetate

$P_A^o$ = vapor pressure of ethyl acetate

Given:

Relative saturation = 50 % = 0.5

Vapor pressure of ethyl acetate = 16 kPa

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

$0.5=\frac{P_A}{16kPa}$

$P_A=8kPa$

Now we have to calculate the molar saturation.

The formula used for molar saturation is:

$\text{Molar saturation}=\frac{P_{vapor}}{P_{\text{vapor free}}}$

and,

P(vapor free) = Total pressure - Vapor pressure

P(vapor) = $P_A$ = 8 kPa

So,

P(vapor free) = 100 kPa - 8 kPa = 92 kPa

The molar saturation will be:

$\text{Molar saturation}=\frac{P_{vapor}}{P_{\text{vapor free}}}$

$\text{Molar saturation}=\frac{8kPa}{92kPa}=0.087$

Therefore, the molar saturation is 0.087

5 0

3 years ago