Klincewicz method

Key takeaways

Klincewicz method belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Klincewicz method to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Klincewicz method from memory before moving on to harder problems.

Reference excerpt

In thermodynamic modelling, the Klincewicz method is a predictive method based both on group contributions and on a correlation with some basic molecular properties. The method estimates the critical temperature, the critical pressure, and the critical volume of pure components. It is named after Karen Klincewicz Gleason who developed it in 1984 in collaboration with Robert C. Reid.

Model description As a group contribution method the Klincewicz method correlates some structural information of a chemical molecule with the critical data. The used structural information are small functional groups which are assumed to have no interactions. This assumption makes it possible to calculate the thermodynamic properties directly from the sums of the group contributions. The correlation method does not even use these functional groups, only the molecular weight and the number of atoms are used as molecular descriptors. The prediction of the critical temperature relies on the knowledge of the normal boiling point because the method only predicts the relation of the normal boiling point and the critical temperature and not directly the critical temperature. The critical volume and pressure however are directly predicted.

Model quality The quality of the Klincewicz method is not superior to older methods, especially the method of Ambrose gives somewhat better results as stated by the original authors and by Reid et al. The advantage of the Klincewicz method is that it is less complex. The quality and complexity of the Klincewicz method is comparable to the Lydersen method from 1955 which has been used widely in chemical engineering. The aspect where the Klincewicz method is unique and useful are the alternative equations where only very basic molecular data like the molecular weight and the atom count are used.

Deviation diagrams The diagrams show estimated critical data of hydrocarbons together with experimental data. An estimation would be perfect if all data points would lie directly on the diagonal line. Only the simple correlation of the Klincewicz method with the molecular weight and the atom count have been used in this example.

Equations Klincewicz published two sets of equations. The first uses contributions of 35 different groups. These group contribution based equations are giving somewhat better results than the very simple equations based only on correlations with the molecular weight and the atom count.

Group-contribution-based equations

T c = 45.40 − 0.77 ∗ M W + 1.55 ∗ T b + ∑ j = 1 35 n j Δ j {\displaystyle T_{c}\,=\,45.40-0.77*MW+1.55*T_{b}+\sum _{j=1}^{35}n_{j}\Delta _{j}}

( M W / P c ) 1 / 2 = 0.335 + 0.010 ∗ M W + ∑ j = 1 35 n j Δ j {\displaystyle (MW/P_{c})^{1/2}\,=\,0.335+0.010*MW+\sum _{j=1}^{35}n_{j}\Delta _{j}}

V c = 25.2 + 2.80 ∗ M W + ∑ j = 1 35 n j Δ j {\displaystyle V_{c}\,=\,25.2+2.80*MW+\sum _{j=1}^{35}n_{j}\Delta _{j}}

Equations based on correlation with molecular weight and atom count only

T c = 50.2 − 0.16 ∗ M W + 1.41 ∗ T b {\displaystyle T_{c}\,=\,50.2-0.16*MW+1.41*T_{b}}

( M W / P c ) 1 / 2 = 0.335 + 0.009 ∗ M W + 0.019 A {\displaystyle (MW/P_{c})^{1/2}\,=\,0.335+0.009*MW+0.019A}

V c = 20 + 0.088 ∗ M W + 13.4 ∗ A {\displaystyle V_{c}\,=\,20+0.088*MW+13.4*A}

with

Group contributions

The group XCX is used to take the pairwise interaction of halogens connected to a single carbon into account. Its contribution has to be added once for two halogens but three times for three halogens (interactions between the halogens 1 and 2, 1 and 3, and 2 and 3).

Example calculations

Example calculation for acetone with group contributions

*used normal boiling point Tb= 329.250 K

Example calculation for acetone with molecular weight and atom count only Used molecular weight: 58.080 g/mol Used atom count: 10

For comparison, experimental values for Tc, Pc and Vc are 508.1 K, 47.0 bar and 209 cm3/mol, respectively.

References

Illustrations

Worked examples

Example 1 — a first encounter with Klincewicz method

Start with the simplest possible case. Write down what Klincewicz method claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Klincewicz method before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Klincewicz method ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Klincewicz method

In research: Klincewicz method appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Klincewicz method in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Klincewicz method is common in secondary-school and first-year university syllabi. It links to neighbouring topics Thermodynamic models, so understanding it makes those chapters shorter.
In everyday life: Look for Klincewicz method outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Klincewicz method in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Klincewicz method means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Klincewicz method out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Klincewicz method in simple terms?

In thermodynamic modelling, the Klincewicz method is a predictive method based both on group contributions and on a correlation with some basic molecular properties. The method estimates the critical temperature, the critical pressure, and the critical volume of pure components.

Why does Klincewicz method matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Klincewicz method?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Klincewicz method.