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The programme uses mechanical analogies to examine the idea that chemical equilibrium exists when the Gibbs function for a system is a minimum.
Metadata describing this Open University video programme
Module code and title: ST294, Principles of chemical processes
Item code: ST294; 09
First transmission date: 09-06-1975
Published: 1975
Rights Statement:
Restrictions on use:
Duration: 00:24:21
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Producer: Andrew Millington
Contributors: Rod Macdonald; Kiki Warr
Publisher: BBC Open University
Keyword(s): Constant temperature bath; Distributional component; Enthalpy; Entropy; Flasks; Gibbs function; Reaction; Royal Institution; Rubber hose
Footage description: Kiki Warr introduces the programme. She performs demonstrations of three simple reactions. All three proceed on their own accord. Kiki Warr sets up a simple mechanical analogy a block sliding down a slope, to show that it is possible to attribute a "downhill" character to chemical reactions such as those above. Kiki Warr then contrasts these with the reverse reaction. This would appear to have an "uphill" character as the magnesium oxide is a stable white powder. Kiki Warr next defines the Gibbs function which will be used to rationalise the "uphill downhill" intuition. Rod McDonald uses a sliding model to examine the sliding block analogy in more detail. He sets up the model in chemical rather than mechanical terms and arrives at a prediction for the course of reactions based on this. Kiki Warr performs a simple laboratory demonstrations. This reaction shows the fallacy of the conclusion arrived at with the mechanical model above. Rod McDonald constructs a curve which accounts for the observed behaviour of the system. He explains how the shape of the curve is arrived at. Graphics showing the necessary data for the construction of the curve, are used. Kiki Warr uses a graph showing three curves. She goes on to consider the curves in greater detail. Kiki Warr demonstrates a physical model of the reaction - a length of rubber tubing suspended between two posts. The model shows how the minimum shifts in response to a variation in the height between two extremes. Kiki Warr and then Rod McDonald discuss the shape of the G curve in relation to the definition of the Gibbs function in terms of enthalpy and entropy. He uses a sliding model again. Short film clip shows Prof. Sir George Porter demonstrating his mechanical model which shows that the position of equilibrium, in a system at constant temperature and pressure, is the result of a competition between an energy term and an entropy term. Rod McDonald sums up.
Master spool number: 6HT/71622
Production number: 00525_1160
Videofinder number: 2753
Available to public: no