A. Variables, this is because you can choose what you're testing
Answer:
one star
In our solar system, there is only one star that we know of – the sun! Our solar system is very unique in that is only has one star. Most other solar systems have at least two stars. These are called binary systems.
Explanation:
Answer:
197.8 J/(mol•K).
Explanation:
- ∆S° = [Σ bS° products] - [Σ aS° reactants], where b and a are the coefficients of the products and the reactants in the balanced reaction equation.
<em>Br₂(l) ⟶ 2 Br(g)</em>
∴ ∆S° = [2 x S° Br(g)] - [S° Br₂(l)]
∴ ∆S° = [(2)(175.0 J/(mol•K)] - [152.2 J/(mol•K)] = 197.8 J/(mol•K).
Boron trichloride has a simple molecular structure,
whereas sodium chloride has a giant ionic lattice
structure. The ionic bonding between oppositely
charged ions in NaCl is stronger than the covalent
intramolecular bonding in BCl3. Therefore, less energy
is required to break the intramolecular covalent bonds in
BCl3, hence a lower melting temperature.
Answer:
-625 kcal/mol
Explanation:
The method to solve this question is based on Hess´s law of constant heat of summation which allows us to combine the enthalpies of individual reactions for which we know their enthalpy to obtain the enthalpy change for a desired reaction.
We are asked to calculate the standard enthalpy of formation of combustion of an unbranched alkane :
CnHn+2 unbranched + O₂ ⇒ CO₂ + H₂O ΔcHº = ?
where CnH2n+2 is the general formula for alkanes.
and we are given information for
n C+ (2n + n)/2 H₂ ⇒ CnHn+2 unbranched ΔfHº = -35 kcal/mol (1)
n C+ (2n + n)/2 H₂ ⇒ CnHn+2 branched ΔfHº = -28 kcal/mol (2)
CnHn+2 branched + O₂ ⇒ CO₂ + H₂O ΔcHº = -632 kcal/mol (3)
If we reverse (1) and add it to the sum (2) and (3) we get the desired equation for the combustion of the unbranched alkane:
CnHn+2 unbranched + O₂ ⇒ CO₂ + H₂O
Thus
ΔcHº unbranched = + 35 kcal/mol + (-28 kcal/mol) + (-632 kcal/mol)
= -625 kcal/mol
