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How do I calculate the 'potential?' resistance in a tube, in cm H2O. I'm a physiotherapist and do positive expiratory pressure breathing exercises with lung patients. Problem, the PEP masks are quite expensive, so we make 'blow bottles' - simply a 1 litre bottle, half filled with water (about 10 cm), with a nice thick (about 1 cm diameter) silicone tubing of about 20 cm, through which the patient blows into the water to make it bubble. Another problem - blowing into the water retains the lung pathogens in the water where they can proliferate. I'd like to use the straw as it is to avoid a contamination source, but would like to know what resistance it will give during expiration. If I have a formula, I can use thinner straws or simply make them longer/shorter for +- specific requirements. (I realise the speed of expiration will also play a role in the resistance.) The resistance we're looking for is from 7 - 30 cm H2O. Thanks!

What is the standard entropy change for the each of the following reactions at 25 degrees C? a. 2 Na(s) + 2H20 (l) ----> 2NaOH (aq) + H2 (g) b. NaCO3 (s) + @HCl (aq) ----> 2NaCl (aq) + H20 (l) + CO2 (g) Comment on the sign of: delta r S degrees (sorry, don't know how to represent it?)

What is the standard entropy change for the each of the following reactions at 25 degrees C? a. 2 Na(s) + 2H20 (l) ----> 2NaOH (aq) + H2 (g) b. NaCO3 (s) + @HCl (aq) ----> 2NaCl (aq) + H20 (l) + CO2 (g) Comment on the sign of: delta r S degrees (sorry, don't know how to represent it?)

Standard enthalpy of formation: Species Enthalpy (kJ/Mol) Br(g) 111.9 Br2 (l) 0 Br2 (g) 30.9 What is the standard enthalpy of vaporization of bromine? What is the energy neede for the reaction Br2 (g) ---> 2Br (g), i.e. the Br -Br bond energy?

Standard enthalpy of formation: Species Enthalpy (kJ/Mol) Br(g) 111.9 Br2 (l) 0 Br2 (g) 30.9 What is the standard enthalpy of vaporization of bromine? What is the energy neede for the reaction Br2 (g) ---> 2Br (g), i.e. the Br -Br bond energy?