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3 years ago

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Which statement is true about energy? A. Energy never moves. B. Energy is never destroyed. C. Energy always changes to heat. D.

Energy always changes to light.

1 answer:

vazorg [7]3 years ago

7 0

B. Energy is never destroyed.

This is stated in the Law of Conservation of Energy.

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An unknown sample weighing 0.3512g was added to 20.0 mL of cyclohexane. The density of cyclohexane is 0.779g/mL, and the freezin

rjkz [21]

Explanation:

It is known that density is mass of a substance divided by its volume.

Mathematically, Density = $\frac{mass}{volume}$

Therefore, calculate the mass of cyclohexane as follows.

mass of cyclohexane = Density × volume

= $0.779 g/mL \times 20 mL$

= 15.58 g

or, = 0.01558 kg (as 1 kg = 1000 g)

As, K_{f} of cyclohexane = $20^{o}C/m$

$\Delta T_{f} = K_{f} \times molality$

$5.2 = 20 \times molality$

molality = $\frac{5.2}{20}$

= 0.26 m

Also, molality is the number of moles of solute present in kg of solvent.

Mathematically, molality = $\frac{\text{no. of moles}}{\text{mass of solvent}}$

0.26 = $\frac{\text{no. of moles}}{0.01558}$

No. of moles = $4.05 \times 10^{-3}$

As, No. of moles = $\frac{mass}{\frac{molar mass}}$

$4.05 \times 10^{-3} = \frac{0.3512}{\text{molar mass}}$

molar mass = 87.0 g/mol

Thus, we can conclude that molar mass of unknown substance is 87.0 g/mole.

4 0

3 years ago

What kind of solid is crystalline boron

Ulleksa [173]

Answer:

It is a network solid, a lattice of many covalent bonds (like diamond, except that it is black rather than transparent).

Explanation:

7 0

3 years ago

Which bases can deprotonate acetylene? the pka values of the conjugate acids are given in parentheses. select all that apply. ch

Usimov [2.4K]

pKa is a value which is related to the acid dissociation constant Ka

pKa = -log Ka

i.e. Ka = 10^-pKa

The deprotonation reaction of acetylene is:

HC≡CH ↔ HC≡C⁻ + H⁺

pKa (HC≡CH) = 25

Solvents with pKa greater than 25 will deprotonate acetylene.

Ans: CH2=CH⁻ pka = 44 and CH3NH⁻ pka = 40

4 0

4 years ago

What happens when a salt reacts with base?

harkovskaia [24]

Answer:

When an acid and a base are placed together, they react to neautralise the acid and base properties, thus making a salt.

Explanation:

The compound formed by the caption of the base and the anion of the acid is called a salt.

4 0

3 years ago

Read 2 more answers

For which type of titration will the ph be basic at the equivalence point?

Pavel [41]

Answer:

weak acid

Explanation:

3 0

3 years ago