Giving justification. categorise the following molecules / ions as nucleophite or electrophite. Hs, Bf3,C2H5O, N , Cl, Ch3-c = O, H2N:, No2
Answers
Answer:
Thermite Reaction: aluminum reacts with iron(III) oxide
The reaction of iron (III) oxide and aluminum is initiated by heat released from a small amount "starter mixture". This reaction is an oxidation-reduction reaction, a single replacement reaction, producing great quantities of heat (flame and sparks) and a stream of molten iron and aluminum oxide which pours out of a hole in the bottom of the pot into sand.
The balanced chemical equation for this reaction is:
2 Al(s) + Fe2O3(s) --> 2Fe(s) + Al2O3(s) + 850 kJ/mol
Curriculum Notes
This chemical reaction can be used to demonstrate an exothermic reaction, a single replacement or oxidation-reduction reaction, and the connection between ∆H calculated for this reaction using heats of formation and Hess' Law and calculating ∆H for this reaction using qrxn = mc∆T and the moles of limiting reactant. This reaction also illustrates the role of activation energy in a chemical reaction. The thermite mixture must be raised to a high temperature before it will react.
To determine how much thermal energy is released in this reaction, heats of formation values and Hess' Law can be used.
http://www.ilpi.com/genchem/demo/thermite/index.html
Substance deltaHfo (kJ/mol)
Fe2O3(s) -822.2
Al(s) 0
Al2O3(s) -1,669.8
Fe (s) 0
By definition, the deltaHfo of an element in its standard state is zero.
2 Al(s) + Fe2O3(s) --> 2Fe (s) + Al2O3 (s)
The deltaH for this reaction is the sum of the deltaHfo's of the products - the sum of the deltaHfo's of the reactants (multiplying each by their stoichiometric coefficient in the balanced reaction equation), i.e.:
deltaHorxn = (1 mol)(deltaHfoAl2O3) + (2 mol)(deltaHfoFe) - (1 mol)(deltaHfoFe2O3) - (2 mol)(deltaHfoAl)
deltaHorxn = (1 mol)(-1,669.8 kJ/mol) + (2 mol)(0) - (1 mol)(-822.2 kJ/mol) - (2mol)(0 kJ/mol)
deltaHorxn = -847.6 kJ
The melting point of iron is 1530°C (or 2790°F).
Learning Objectives
1. The chemical reaction in this demonstration is an example of an exothermic reaction, ∆Hrxn is negative.
2. In order to initiate this reaction, an activation energy (heat) must be supplied.
3. The chemical reaction releases heat and the "surroundings" gain heat.
4. Heats of formation values, ∆H°f, can be used to calculate ∆H of this reaction using Hess' Law.
5. ∆H of this reaction can be estimated by measuring the mass of the thermite mixture, and knowing the initial and final temperature and the specific heat, calculating qreaction, then calculating ∆H reaction.
6. This reaction illustrate the metallurgy of iron.
This demonstration may only be performed by a trained chemistry lecture demonstrator. The chemical reaction in this demonstration is very exothermic and extreme safety measures must be followed to minimize the risk to members of the audience. Use only the minimum amount of reactants appropriate to illustrate the reaction. Allow about 10 minutes to perform this demo.
One day of lead time is required for this project.
Discussion
The equation for this reaction is: 2 Al(s) + Fe2O3(s) --> 2Fe (s) + Al2O3 (s). The large decrease in the energy of the system is a consequence of the high charge concentration on the aluminum ion due to its small size. The oxide ions can approach the aluminum ion more closely than than they can approach the ferric ion. Thus coulombic forces stabilize the aluminum oxide relative to the ferric oxide. The enthalpy change of this reaction is about -850 kJ/mol! The heat generated melts the iron and the aluminum oxide which pour out of the hole in the bottom of the pot. While they are liquid, they will usually separate out with the denser iron sinking to the bottom of the"puddle." After the liquid has solidified and cooled enough to handle, the aluminum oxide "slag" can usually be broken off of the iron, sometimes by simply dropping it on the floor a few times.