48. Solution to Chemistry Problem

9. Construct a phase diagram (melting diagram for system A – B) based on the data on the crystallization onset temperature of a two-component system given in Table 2. Perform the following tasks using the diagram:
1) Mark with dots: I – liquid melt containing a% of substance A at temperature T1; II – melt containing a% of substance A in equilibrium with crystals of a chemical compound; III – a system consisting of solid substance A in equilibrium with a melt containing b% of substance A; IV – equilibrium of phases of the same composition; V – equilibrium of three phases;
2) determine the compositions of chemical compounds;
3) determine the qualitative and quantitative compositions of eutectics;
4) plot all types of cooling curves possible in a given system; indicate which compositions on the diagram these curves correspond to;
5) in what physical state are the systems containing b, g, d% of substance A at temperature T1 (see Table 3)? What will happen to these systems if they are cooled to temperature T2;
6) determine the number of phases and the number of thermodynamic degrees of freedom of the system at the eutectic temperature and content of A: a) 95 mol. %; b) 20 mol. %;
7) at what temperature will the melt containing b% of substance A begin to solidify? At what temperature will it solidify completely? What is the composition of the first crystals that fall out;
8) at what temperature will the alloy containing g% of substance A begin to melt? At what temperature will it melt completely? What is the composition of the first drops of the melt;
9) calculate the heats of fusion of substances A and B;
10) what component and in what quantity will crystallize if 2 kg of the melt containing a% of substance A is cooled from T1 to T2?

Table 2

No. of options System Composition A,
mol. % T of the beginning of crystallization, K
9
A – PbCl2
B – SrCl2

0
10
20
30
40
45
50
55
65
70
75
80
90
100 1147
1089
1004
906
964
975
978
969
896
827
853
879
960
999

Table 3

No. of var. T1, K A b c d D T2, K
9
1073
35
85
5
50
85
923