Hess's Law

Question 1

How many J in 1 kJ?

Answer 1

1000

Question 2

How do you calculate ∆H?

Answer 2

1) Balance equation
2) Calc. amount of moles of each reactant & ignore the one that is in excess

Question 3

Equation for ∆H

Answer 3

∆H = Q/moles

Question 4

50cm3 of 1.0moldm-3 HCl added to 50cm3 of 1.0moldm-3 NaOH solution. Temp rose by 6.8°C. Calculate enthalpy of neutralisation for this reaction. Assume that density of solution is 1.00gcm-3, the specific heat capacity is 4.18Jg-1K-1

Answer 4

Q = mc∆T
m= 50+50=100
c=4.18
∆T=6.8
Q = 100 x 4.18 x 6.8 = 2842J
∆H = Q/mol
Mol HCl = conc x vol = 1.0 x (50/1000) = 0.050
Mol NaOh = conc x vol = 1.0 x (50/1000) = 0.050
2842/1000 = 2.842kJ
HCl + NaOh —> NaCl + H2O
∆H = -2.842/0.050 = -56.8kJmol-1

Question 5

What is the principle of the conservation of energy?

Answer 5

Energy can neither be created/destroyed but can be converted from 1 form to another

Question 6

What happens to the stability of the compound as the standard state of formation gets more negative?

Answer 6

Gets more stable

Question 7

5 bonding pairs, 1 lone pair

Answer 7

Square pyramid