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3 years ago

Which of these substances are elements?

2 answers:

8 0

An element is a species of atom that has the same amounts of electrons and protons in their nuclei. To know which of these substances are elements, we can look it up in the periodic table of elements. The elements are as follows:

1.silicon
2.lead
3.silicone
5.iodine

Andru [333]3 years ago

8 0

Answer is:

1. silicon.

2. lead.

5. iodine.

Silicon (symbol: Si) is an element with atomic number 14 (14 protons).

Lead (Pb) is an element with atomic number 82.

Iodine (I) is an element with atomic number 53.

Silicone is a compound (polymer) made of silicon, oxygen, hydrogen, carbon and other elements.

Quartz is a compound (mineral) made of silicon and oxygen atoms.

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2.50 L of a gas at standard temperature and pressure is compressed to 575 mL. What is the new pressure of the gas

vfiekz [6]

Answer:

4.35 atm

Explanation:

According to the information given;

Initial volume of the gas, V₁ is 2.50 L
Initial pressure of the gas is standard pressure P₁, normally 1 atm
New volume of the gas, V₂ is 575 mL

We are required to determine the new pressure of the gas, P₂ ;

To answer the question, we are going to use the Boyle's law, that relates pressure and volume at constant temperature.

According to Boyle's law;

P₁V₁ = P₂V₂

Therefore, to determine the new pressure, P₂, we rearrange the formula;

New pressure, P₂ = P₁V₁ ÷ V₂

Thus;

P₂ = ( 1 atm × 2.50 L) ÷ 0.575 L

= 4.3478 atm

= 4.35 atm

Therefore, the new pressure of the gas is 4.35 atm

6 0

3 years ago

Read 2 more answers

commercial cold packs consist of solid NH4NO3 and water. In a coffee-cup calorimeter, 5.60g NH4NO3 is dissolved in 100g of water

fgiga [73]

Answer:

-1.37 kJ/mol

Explanation:

The expression for the calculation of the enthalpy of dissolution of [tex[NH_4NO_3[/tex] is shown below as:-

$\Delta H=m\times C\times \Delta T$

Where,

$\Delta H$ is the enthalpy of dissolution of [tex[NH_4NO_3[/tex]

m is the mass

C is the specific heat capacity

$\Delta T$ is the temperature change

Thus, given that:-

Mass of ammonium nitrate = 5.60 g

Specific heat = 4.18 J/g°C

$\Delta T=17.9-22.0\ ^0C=-4.1\ ^0C$

So,

$\Delta H=-1.25\times 4.18\times 3.9\ J=-95.9728\ J$

Negative sign signifies loss of heat.

Also, 1 J = 0.001 kJ

So,

$\Delta H=-0.096\ kJ$

Also,

Molar mass of [tex[NH_4NO_3[/tex] = 80.043 g/mol

The formula for the calculation of moles is shown below:

$moles = \frac{Mass\ taken}{Molar\ mass}$

Thus,

$Moles= \frac{5.60\ g}{80.043 \ g/mol}$

$Moles= 0.06996\ mol$

Thus, $\Delta H=-\frac{0.096}{0.06996}\ kJ/mol=-1.37\ kJ/mol$

6 0

3 years ago

Which of the following is true for the actual yield of a reaction?

ludmilkaskok [199]

Answer:

It is always less than the theoretical yield

Explanation:

For many chemical reactions, the actual yield is usually less than the theoretical yield. This is due to possible loss in the process or inefficiency of the chemical reaction.

4 0

3 years ago

Read 2 more answers

Sterling silver contains silver and copper metals. If a sterling silver chain contains 33.3 g of silver and 2.70 g of copper, wh

marusya05 [52]

Answer:

7.5 % of Ag

Explanation:

Total mass of sterling silver chain is:

Mass of silver + Mass of copper

33.3 g Ag + 2.70g of Cu = 36 g

% of Silver is (mass of silver / total mass) . 100 →