All categories

3 years ago

A rock _____ can get polished from water running over it?

Chemistry

2 answers:

Musya8 [376]3 years ago

6 0

Answer:

The answer is: B

Explanation:

The reason for this is because when a rock is underwater (the river, in this case), the water runs across it non-stop until the rock is removed from the water. The only way it can be polished if it is submerged under the water for quite some time (years and years).

I hope this helped! :))

puteri [66]3 years ago

3 0

Answer:

The answer is B. A river is a body of water, therefore, there will always be some water running over the rock.

You might be interested in

All matter has thermal energy because atoms are constantly

ololo11 [35]

The atoms are constantly in motion

3 0

3 years ago

Reaction of 0.028 g of magnesium with excess hydrochloric acid generated 31.0 mL of hydrogen gas. The gas was collected by water

MA_775_DIABLO [31]

Explanation:

(a) It is given that magnesium is reacted with hydrochloric acid and the hydrogen evolved is collected at top. This means that hydrochloric acid will be present in a solution (HCl + Water) and the solvent will be water.

Due to evaporation some amount of water will have evaporated and would be present in vapor phase. Therefore, when the reaction occurs only hydrogen will not be present in vapor phase but, will be accompanied by water vapors as well .

Hence, Dalton's law the total pressure of the system will be sum of pressure exerted by hydrogen gas and pressure exerted by water vapors .

Let us assume that the partial pressure of hydrogen gas be " $P_H_{2}$ "

And, the partial pressure of water will be nothing but the vapor pressure of water,

Vapor pressure of water = $P_{water}$

= 19.8 mm Hg

Total pressure of the system = 746 mm Hg

Total pressure = $P_H_{2} + P_{water}$

746 = $P_H_{2}$ + 19.8

or, $P_H_{2}$ = 746-19.8

= 726.2 mm Hg

Hence, partial pressure of hydrogen gas is 726.2 mm Hg.

(b) To calculate volume at STP, we will first calculate at $22^{o}C$ and 726.2 mm Hg and than convert it to STP conditions.

Therefore, to calculate volume at $22^{o}C$ and 726.2 mm Hg we will make use of ideal gas law as follows.

P = 726.2 mm Hg

= $\frac{726.2}{760}$

= 0.955 atm

T = $22^{o}C$

= 22+273.15 = 295.15 K

V = 31 ml = $31 \times 10^{-3}$ Litre

According to the ideal gas law ,

PV = nRT

where, P = pressure of the system ,

V = volume of the gas

N = number of moles

R = 0.0821 liter atm/mole K

T = Temperature

Hence, putting the given values into the above formula as follows.

$0.955 \times 31 \times 10^{-3} = N \times 0.0821 \times 295.15$

N = $1.222 \times 10^{-3}$ moles

Now, the moles of hydrogen won't change. Therefore, let us calculate volume at STP of $1.222 \times 10^{-3}$ moles of hydrogen.

Now, at STP T = 273.15 K , P = 1 atm and N = $1.222 \times 10^{-3}$ moles

$1 \times V = 1.222 \times 10^{-3} \times 0.0821 \times 273.15 K$

V = 0.027398 Litre

= $0.027398 \times 1000$ (as 1 L = 1000 ml)

= 27.398 ml

Therefore, volume of hydrogen at STP is 27.398 ml .

(c) Now, we can write the the reaction for this case as follows.

$Mg + 2HCl \rightarrow MgCl_{2} + H_{2}$

As, weight of magnesium = 0.028 grams

Molar mass of magnesium = 24.3 grams/mole

Number of moles of magnesium = $\frac{mass}{\text{molar mass}}$

= $\frac{0.028}{24.3}$

= $1.15226 \times 10^{-3}$ moles

Since, it can be seen from the reaction that

1 mole of Magnesium = 1 mole of hydrogen

and, moles of hydrogen = $1.15226 \times 10^{-3}$ moles

= 0.001523 moles

Hence, theoretical number of moles of hydrogen that can be produced from 0.028 grams of Mg is 0.001523 moles

8 0

4 years ago

How do i found out how animals gain energy and from where

otez555 [7]

Answer:

Animals gain energy from the food they eat. Some animals eat plants while others eat other animals. This is passing of energy from the sun to plants to animal to other animals is called a food chain

6 0

3 years ago

Enter your answer in the provided box. To draw a Lewis structure, first add the number of outer (valence) electrons contributed

DIA [1.3K]

Answer:

14 is this value for a molecule of $CH_3Cl$ .

Explanation:

Lewis-dot structure : It shows the bonding between the atoms of a molecule and it also shows the unpaired electrons present in the molecule.

In the Lewis-dot structure the valance electrons are shown by 'dot'.

Number of total outer valence electrons is carbon = 4

Number of total outer valence electrons is hydrogen = 1

Number of total outer valence electrons is chlorine = 7

For total number of outer electrons is $CH_3Cl$

$=1\times 4+3\times 1+1\times 7=14$

14 is this value for a molecule of $CH_3Cl$ .

4 0

4 years ago

A 35.6 g sample of ethanol (C2H5OH) is burned in a bomb calorimeter, according to the following reaction. If the temperature ros

PilotLPTM [1.2K]

<h3>Answer:</h3>

1.24 × 10³ kJ/mol

<h3>Explanation:</h3>

From the question we are given;

Heat capacity of the calorimeter =23.3 kJ/°C

Temperature change, ΔT = 76°C - 35°C

= 41 °C

Mass of ethanol = 35.6 g

Molar mass of ethanol = 46.07 g/mol

We are required to determine the molar enthalpy

We can use the following steps:

<h3> Step 1 : Calculate the heat change of the reaction</h3>

Heat change will be equivalent to heat gained by the calorimeter.

Therefore;

Heat = heat capacity × change in temperature

Q = CΔT

= 23.33 kJ/°C × 41°C

= 955.3 kJ

<h3>Step 2 : Calculate the moles of ethanol burned </h3>

Moles = mass ÷ Molar mass

Therefore;

Moles of ethanol = 35.6 g ÷ 46.07 g/mol

= 0.773 moles

<h3>Step 3: Calculate the molar enthalpy of the reaction </h3>

Heat change for 0.773 moles of ethanol is 955.3 kJ

0.773 moles = 955.3 kJ

1 mole will have ,

= 955.3 kJ ÷ 0.773 moles

= 1235.83 kJ/mol

= 1.24 × 10³ kJ/mol

But since the reaction is exothermic (release of heat) then the enthalpy change will have a negative sign.

Thus;

ΔH = -1.24 × 10³ kJ/mol

7 0

4 years ago