Answer to Question #309245 in General Chemistry for Ayen

Question

First Law of Thermodynamics and Calorimetry

A gas system with constant pressure has change in internal energy of 240 J. Heat was lost to the surroundings and 150 J work was done to the surroundings as well. How many calories of heat was lost?

315 moles of butane (C4H10) was burned in a copper calorimeter containing 5065 g of water. The calorimeter weighs 2,800 g. The temperature was observed to increased by 3.15 °C. Calculate the molar heat of combustion of butane. The specific heat of copper and water are 0.386 J/g. °C and 4.18 J/g. °C respectively.

A 60-g silver spoon (specific heat 0.233 J/g °C) at 25 °C is placed in 180 g of coffee at 85 °C and the temperature of the two become equal. What is the final temperature when the two become equal? The coffee has specific heat of 5.12J/g. °C.

Answer 1

Applying the first law of thermodynamics to a system when is heat a positive quantity?

It means any heat transfer that increases the energy of a system is positive, and heat transfer that decreases the energy of a system is negative. Fig. 1: Sign convention: positive if to the system, negative if from the system. Heat can be transferred in three different modes conduction, convection, and radiation.