Carbon can form four covalent bonds.
Hydrogen can form one covalent bond.
Nitrogen can form three covalent bonds.
Oxygen can form two covalent bonds.
Answer:
True
Explanation:
The physical changes are reversible in most cases and these changes are not the chemical changes which means that it is only the change in its state not in their nature. Just take the example of water, on cooling it becomes solid and change in color can be seen which is white in solid form and colorless in liquid form. This is also reversible and is a physical change. This means that physical changes can be identified at macroscopic level. Hence the answer is true.
The new pressure, P₂ is 6000 atm.
<h3>Calculation:</h3>
Given,
P₁ = 1.5 atm
V₁ = 40 L = 40,000 mL
V₂ = 10 mL
To calculate,
P₂ =?
Boyle's law is applied here.
According to Boyle's law, at constant temperature, a gas's volume changes inversely with applied pressure.
PV = constant
Therefore,
P₁V₁ = P₂V₂
Put the above values in the equation,
1.5 × 40,000 = P₂ × 10
P₂ = 1.5 × 4000
P₂ = 6000 atm
Therefore, the new pressure, P₂ is 6000 atm.
Learn more about Boyle's law here:
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The enthalpy of reaction for the combustion of ethane 2CH₃CH₃ + 7O₂ → 4CO₂ + 6H₂O calculated from the average bond energies of the compounds is -2860 kJ/mol.
The reaction is:
2CH₃CH₃ + 7O₂ → 4CO₂ + 6H₂O (1)
The enthalpy of reaction (1) is given by:
(2)
Where:
r: is for reactants
p: is for products
The bonds of the compounds of reaction (1) are:
- 2CH₃CH₃: 2 moles of 6 C-H bonds + 2 moles of 1 C-C bond
- 7O₂: 7 moles of 1 O=O bond
- 4CO₂: 4 moles of 2 C=O bonds
- 6H₂O: 6 moles of 2 H-O bonds
Hence, the enthalpy of reaction (1) is (eq 2):

Therefore, the enthalpy of reaction for the combustion of ethane is -2860 kJ/mol.
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I hope it helps you!
Water moved through the water cycle by changing its state. Think, for example, of water evaporating (liquid to gas), snow sublimating (solid to gas) or melting (solid to liquid), rain (gas to liquid), sleet (liquid to solid), or snow (gas to solid).
The answer would thus be A.