Question

Q1/50 grams of an unknown metal at a temperature of 100 ºC is placed in a calorimeter that holds 25.0 grams of cold water (10 ºC). After 10 minutes, the temperature of the mixture stabilizes at 24 ºC. What is the specific heat capacity of the unknown metal? (Specific heat of water is 4.184 J  g 1  C1 ) a. 0.496 J d. 0.335 J b. 0.421 J e. 0.689 J c. 0.385 J

the answer is B 0.421 J but i dont know how?

Q2/ How many grams of methane must be burned to produce 1000 kJ of energy, according to the following reaction:: CH4  2O2 CO2  2H2O H = –890.4 kJ a. 90 g d. 18 g b. 9 g e. 38 g

The answer is D 18g but i dont know how

Answer 1

1) heat lost by metal = heat gained by water

         m1*s1*DT1 = m2*s2*DT2

m1 = mass of metal = 50 g

s1 = specific heat of metal = ?

DT = 100-24 = 76 c

m2 = mass of water = 25 g

s2 = specific heat of water = 4.184 j/g.c

DT2 = 24-10 = 14

50*S1*76 = 25*4.184*14

S1 = specific heat of metal = 0.385 j/g.c

answer: c.0.385 j/g.c

2)

according to reaction: 1 mol CH4 = 890.4 Kj

SO That, No of mol of CH4 required = 1000/890.4

                                     = 1.123 mol

amount of CH4 required = n*Mwt

                       = 1.123*16

                       = 17.968 g

                       = 18 g
answer: d. 18 g