An average convective heat transfer coefficient for flow of 100 °C air over a flat plate is measured by observing the temperature-time history of a 30 mm thick copper slab (p =9000 kg/m2, e air. In one test run, the initial temperature of the plate was 210 °C, and in 5 minutes the temperature decreased by 40°C. Find the heat transfer coefficient for this case. Neglect internal thermal resistance. [Ans. 77 24 W/m2 °C] c 0.38 kJ/kg °C, k-370 W/m°C). exposed to 100 °C

given:

mass of na = 115 g

excess cl2

to determine:

mass of nacl produced

explanation:

given reaction is-

2na(s) + cl2(g) → 2nacl(s)

since cl2 is in excess, na will be the limiting reagent

as per the reaction stoichiometry na: nacl = 1: 1

i.e. moles of na reacted = moles of nacl formed

now, # moles of na = mass of na/atomic mass

                                  = 115 g/23 g.mol-1 = 5 moles

therefore, moles of nacl = 5

molar mass of nacl = 58 g/mol

mass of nacl = 5 moles * 58 g.mol-1 = 290 g

ans: amount of nacl produced = 290 g