The balanced chemical reaction is written as:
MnCl2(s)+H2SO4(aq)→MnSO4(aq)+2HCl(g)
We are given the amount of hydrochloric acid to be produced in the reaction. This value will be the starting point for the calculations.We do as follows:
.0525 L HCl ( 1 mol / 22.4 L ) ( 1 mol MnCl2 / 2 mol HCl ) (125.84 g / 1 mol ) = 0.15 g MnCl2
The structural formula for 2-methylpentane is in Figure 1. It shows all the C-C and C-H bonds explicitly.
The bond-line formula for 2-methylpentane is in Figure 2. We assume that a carbon atom is at the ends and junctions of the lines. We do not show the H atom, but we mentally assume that there are enough to give each carbon a valence of four.
A condensed structural formula is designed to be typed <em>all on one line</em>. We could write the condensed structural formula for 2-methylpentane as either (CH₃)₂CH-CH₂-CH₂-CH₃ or CH₃CH(CH₃)CH₂CH₂CH₃.
The horizontal C-C bonds are <em>optional </em>— you can include or omit them as desired.
Reaction of calcium with water
Calcium reacts slowly with water. This is in contrast with magnesium, immediately above calcium in the periodic table, which is virtually unreactive with cold water. The reaction forms calcium hydroxide, Ca(OH)2 and hydrogen gas (H2).
ΔHrxn = ΣδΗ(bond breaking) - ΣδΗ(bond making)
Bond enthalpies,
N ≡ N ⇒ 945 kJ mol⁻¹
N - Cl ⇒ 192 kJ mol⁻¹
Cl - Cl⇒ 242 kJ mol⁻¹
According to the balanced equation,
ΣδΗ(bond breaking) = N ≡ N x 1 + Cl - Cl x 3
= 945 + 3(242)
= 1671 kJ mol⁻¹
ΣδΗ(bond making) = N - Cl x 3 x 2
= 192 x 6
= 1152 kJ mol⁻¹
δHrxn = ΣδΗ(bond breaking) - ΣδΗ(bond making)
= 1671 kJ mol⁻¹ - 1152 kJ mol⁻¹
= 519 kJ mol⁻¹