energy calculation qs (1 Viewer)

[s_t_a_r1234]

1. Write the chemical equation and calculate delta H for the reaction which occurs in each of the following
a) when .5g magnesium is burned in air, 12.4 kJ of heat is released
b) when 1.1 g zinc is dissolved in excess hydrochloric acid, 2.6 jk of heat is liberated.
c)when an aqueous solution containing 18. g magnesium chloride is added to an excess of sodium carbonate solution, 9.2 kJ of heat is absorbed.

a) 2Mg(s)+O2->2MgO(s) 2 moles reacted therefore delta H is
- 12.4/2
= -6.2 x 10^3 kJ/mol
b)Zn(s)+2HCl(aq)->ZnCl2(s) +H2(g)
1 : 2 1: 1
mass - 1.1 g ..............!

i know you have to use the q=MC delta T formula i only know it according to the topic of water.. could someone please figure these out for meh thankyou heaps

 

[Dreamerish*~]

These are from the second edition of CC, yes? They have answers at the back if you want to check.

a). 2Mg_(s) + O₂ → 2MgO

n = m/M

n = 0.5/24.3

= 0.021

12.4/0.021 = 602.64 kJ

. : ΔH = -602.64 kJ mol^-1 ( "-" because it's exothermic)

However, in the equation above, we have 2 moles of Mg, so to calculate ΔH for that particular equation, it would be -602.64 x 2 = -1205.28 kJ.

Therefore the ΔH for this particular reaction is -1205.28 kJ.

b). Zn_(s) + HCl_(aq) → ZnCl_(aq) + H_2(g)

n = m/M

n = 1.1/65.4

= 0.017

2.6/0.017 = 154.58 kJ

. : ΔH = -154.58 kJ mol^-1

In this reaction, only one mole of Zn is reacted with HCl, therefore the ΔH for this particular reaction is -154.58 kJ.

c) MgCl_2(aq) + Na₂CO<sub>3(aq) → MgCO3(s) + 2NaCl(aq)

n = m/M

n = 18/95.3

= 0.1889

9.2/0.1889 = 48.71 kJ

. : ΔH = 48.71 kJ mol^-1

In this reaction, only one mole of MgCl2 is reacted with Na2CO3, therefore the ΔH for this particular reaction is 48.71 kJ.

Forgive my rusty preliminary knowledge, but I believe these are correct.</sub>