Answer:
-1815.4 kJ/mol
Explanation:
Starting with standard enthalpies of formation you can calculate the standard enthalpy for the reaction doing this simple calculation:
∑ n *ΔH formation (products) - ∑ n *ΔH formation (reagents)
This is possible because enthalpy is state function meaning it only deppends on the initial and final state of the system (That's why is also possible to "mix" reactions with Hess Law to determine the enthalpy of a new reaction). Also the enthalpy of formation is the heat required to form the compound from pure elements, then products are just atoms of reagents organized in a different form.
In this case:
ΔH rxn = [(2 * -1675.7) - (3 * -520.0)] kJ/mol = -1815.4 kJ/mol
The important thing in this question is the unit. The mass equals density * volume. 3.1 L = 3.1 * 10^3 cm3. So the mass is 3.193*10^3 g. 1 pound = 453.95 g. So the answer is 7.04 pounds.
Answer : The cell emf for this cell is 0.118 V
Solution :
The half-cell reaction is:

In this case, the cathode and anode both are same. So,
is equal to zero.
Now we have to calculate the cell emf.
Using Nernest equation :
![E_{cell}=E^o_{cell}-\frac{0.0592}{n}\log \frac{[Cl^{-}{diluted}]}{[Cl^{-}{concentrated}]}](https://tex.z-dn.net/?f=E_%7Bcell%7D%3DE%5Eo_%7Bcell%7D-%5Cfrac%7B0.0592%7D%7Bn%7D%5Clog%20%5Cfrac%7B%5BCl%5E%7B-%7D%7Bdiluted%7D%5D%7D%7B%5BCl%5E%7B-%7D%7Bconcentrated%7D%5D%7D)
where,
n = number of electrons in oxidation-reduction reaction = 1
= ?
= 0.0222 M
= 2.22 M
Now put all the given values in the above equation, we get:


Therefore, the cell emf for this cell is 0.118 V
<span>(A)hydrochloric acid + silver nitrate
HCl(aq) + AgNO3(aq) -----> AgCl(s) +HNO3(aq)
</span><span>(B)hydrochloric acid + sodium hydroxide
</span><span>HCl(aq) + NaOH(aq) -----> NaCl(aq) + H2O(l)
</span><span>(C)calcium chloride + silver nitrate
CaCl2(aq) + AgNO3(aq) ----> </span>AgCl(s) +Ca(NO3)2(aq)
<span>(D)sodium chloride + silver nitrate
</span>NaCl(aq) + AgNO3(aq) ----> AgCl(s) +NaNO32(aq)
AgCl is a white precipitate.
In (B) no precipitate was formed, so answer is B.
The question is incomplete. Here is the complete question.
An atom of lead has a radius of 154 pm and the average orbitalspeed of the electron in it is about 1.8x
m/s. Calculate the least possible uncertainty in a measurement of the speed of an electron in an atom of lead. Write your answer as a percentage of the average speed, and round it to significant 2 digits.
Answer: v% = 0.21 m/s
Explanation: To calculate the uncertainty, use <u>Heisenberg's Uncertainty Principle</u>, which states that: ΔpΔx≥
where h is <u>Planck's constant</u> and it is equal to 6.626.
m²kg/s.
Since p (momentum) is p = m.v:
mΔv.Δx ≥ 
Δv = 
Given that: r = x = 1.54.
m and mass of an electron is m=9.1.
kg
Δv = 
Δv = 0.0376.
As percentage of average speed:
Δv.
.100% =
.10² = 0.021.10 = 0.21%
The least possible uncertainty in a speed of an electron is 0.21%.