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4 years ago

Help please. The combustion of pentane, C5H12, occurs via the reaction

1 answer:

4 0

If I were you, I'd try to go with this one : $[(6)(-241.8)+(5)(-393.5)]-[-35.1] =-481.6$ . I think that is a solution you have to find. Just use the sum of standard enthalpies of products and of reactants. Hope you will find it helpful!

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Determine the ph of a 0.188 m nh3 solution at 25°c. the kb of nh3 is 1.76 × 10-5.

Ber [7]

When NH3 is dissolved in water, it dissociates partially producing NH4+ ions and OH- ions. It has an equation:
NH3 + H2O → NH4+ + OH-

We use the Kb expression to determine the [OH-] concentration,

Kb = [NH4+] [OH-] /* [NH3] 

We can write NH4+ as OH- since they are of equal ratio.
(1.76*10^-5) = [OH-]² / 0.188
[OH-]² = 3.3088*10^-6 
[OH-] = 1.819*10^-3 

We calculate for H+ concentration as follows:

[H+] [OH-] = 10^-14 
[H+] = 10^-14 / [OH-] 
[H+] = 10^-14 / (1.819*10^-3) 
[H+] = 5.50*10^-12 

pH = -log [H+] 
pH = -log (5.5*10^-12) 
pH = 11.26

4 0

3 years ago

The volume of a carbon atom is 1.9 x 10–30 m3. What is the radius of the atom in picometers? The volume of a sphere is (4/3)(pi)

skelet666 [1.2K]

Volume of sphere = $\frac{4}{3}\pi r^{3}$

where, $\pi$ = $3.14$

r = radius of sphere

Put the given value of volume in above formula i.e. ( $1.9\times 10^{-30}m^{3}$ )

Thus,

$1.9\times 10^{-30}m^{3} = \frac{4}{3}\3.14 r^{3}$

$1.9\times 10^{-30}m^{3} = 4.1867 r^{3}$

$r^{3} = \frac{1.9\times 10^{-30}m^{3}}{4.1867}$

$r^{3} = 0.453\times 10^{-30}m^{3}$

$r = \sqrt[3]{0.453\times 10^{-30}m^{3}}$

= $0.768\times 10^{-10}m$

= $7.68\times 10^{-12}m$

= $7.68 picometers$

Thus, radius of the carbon atom is $7.68 picometers$

6 0

3 years ago

Read 2 more answers

A chemistry student needs to standardize a fresh solution of sodium hydroxide. He carefully weighs out 28.mg of oxalic acid H2C2

Nezavi [6.7K]

Answer:

The molarity of the student's sodium hydroxide solution is 0.0219 M

Explanation:

1) Chemical reaction.

a) Kind of reaction: neutralization

b) General form: acid + base → salt + water

c) Word equation:

sodium hydroxide + oxalic acid → sodium oxalate + water

d) Chemical equation:

NaOH + H₂C₂O₄ → Na₂C₂O₄ + H₂O

b) Balanced chemical equation:

2NaOH + H₂C₂O₄ → Na₂C₂O₄ + 2H₂O

2) Mole ratio

2mol Na OH : 1 mol H₂C₂O₄ :1 mol Na₂C₂O₄ : 2 mol H₂O

3) Starting amount of oxalic acid

mass = 28 mg = 0.028 g
molar mass = 90.03 g/mol
Convert mass in grams to number of moles, n:

n = mass in grams / molar mass = 0.028 g / 90.03 g/mol = 0.000311 mol

4) Titration

Volume of base: 28.4 mL = 0.0248 liter
Concentration of base: x (unknwon)

Number of moles of acid: 2.52 mol (calculated above)

Proportion using the theoretical mole ratio (2mol Na OH : 1 mol H₂C₂O₄)

$\frac{2}{1} =\frac{x}{2.52}\\ \\ \\x=0.000311(2)=0.000622$

That means that there are 0.000622 moles of NaOH (solute)

5) Molarity of NaOH solution

M = n / V (liter) = 0.000622 mol / 0.0284 liter = 0.0219 M

That is the correct number using three signficant figures, such as the starting data are reported.

5 0

3 years ago

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Why is a changing ocean temperature of only one or 2 degrees so concerning? Please help!!!!

Svetllana [295]

Because it throws the earth off balance and if it does it often enough then it will soon add up.

6 0

4 years ago

Read 2 more answers

What is another example of pairing advanced technology with simple machines?

Anvisha [2.4K]

One example could be scanners linked to a networked database. Those little hand scanners that you see at a Publix or Wal-Mart report back to series of systems that allow stores to track inventory across the entire business allowing them to anticipate when they should order more of one item or see what has been selling particularly well -- or not. Consumers don't see any of that when they buy their Count Chocula, but the database systems do and those can be extremely complex. I hope this helps you out!! have a wonerful day!!

8 0

3 years ago