Question

4. Heat transfer: q = mass x Cs x ΔT and –qreaction = +qsolution

a. A piece of metal with a mass of 8.6 g was heated to 100.0°C and dropped into a coffee cup
calorimeter containing 402.4 g of water at 25.0°C. If the temperature of the water and the
metal at thermal equilibrium is 26.4°C, what is the specific heat of this metal in J/g°C?

b. How much heat energy must be added in order to boil a liter of water (initial temperature of
24.0°C) in a 1.0 kg copper pot? The specific heat capacity of water is 4.184 J/g°C and the
specific heat capacity of copper is 0.385 J/g°C.

c. A 50.0 g piece of iron (Tinitial = 225°C) and a 50.0 g piece of gold (Tinitial = 25.0°C) are
brought into contact with each other. Assuming no heat is lost to the surroundings, calculate the
temperature of the two metals when they reach thermal equilibrium. The specific heat
capacity of iron = 0.449 J/g°C and the specific heat capacity of gold = 0.128 J/g°C.

d. A 100.0 mL sample of 0.300 M NaOH is mixed with a 100.0 mL sample of 0.305 M HNO3 in
a coffee cup calorimeter. If both solutions were initially at 25.0°C and the maximum
temperature of the resulting mixture was 28.5°C. Find the heat of the reaction, qreaction, in
joules and report the molar heat of reaction, ΔHreaction, in kJ/mole. The density of both
solutions is 1.00 g/mL and heat capacity is the same as water: 4.184 J/g°C.

Answer 1

a) Given, mass of metal = 8.6 g. Initial temp. of metal = 100 degree c Final temperature = 26.4 degree c Let, specific heat of the metal be c J/g degree c Heat lost by metal in water = 8.6 times c times (100 - 26.4)J. Initial temperature of water = 25 degree c Final temperature of water = 26.4 degree c mass of water = 402.4 g. Heat gained by water = 402.4 times 4.184 (26.4 - 25) Now according to law of conservation of energy, heat lost = heat gained => 402.4 times 4.184 times (26.4 - 25) = 8.6 times c times (100 - 26 - 4) => 2357.1 = 632.96 times c => c = 3.72 Therefore specific heat of the metal is 3.72 J/g degree c b) Initial temperature of the water-pot system = 24 degree c. Water will boil when temperature of both water and copper pot attains 100 degree c So, total heat energy required to boil =