Chemisty help!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

4.) How many grams of silver are there in a ring. If 10.488 kJ of heat are needd to raise the temp. from 30 c to 80 c ?

5.) how much heat does it take to warm 16.0 g of pure water from 90 c to 100 c?

6.) When 45 g of an alloy is dropped into 100g of water at 25 c the final temp is 37 c. What is the specific heat of the alloy?

7.) By what quantity must the heat capacity of an object be divided to obtain the specific heat of that material ?
a.) mass b.) volume c.) temperature d.) energy e.) density

4.) How many grams of silver are there in a ring. If 10.488 kJ of heat are needd to raise the temp. from 30 c to 80 c ?

using specific heat of silver from http://en.wikipedia.org/wiki/Specific_he… as 0.233 J/g-C
dH = m C dT
10,488 Joules = m (0.233 J/g-C) (50C)
m = 900 grams of silver

that's a lot of silver
trying 0.488 kJ gives 41.9 grams of silver
trying 1.488 kJ gives 128 grams of silver


5.) how much heat does it take to warm 16.0 g of pure water from 90 c to 100 c?
dH = m C dT
dH = 16.0 g (4.184 J/g-C)(10 C)
dH = 669 Joules
rounded to 2 sig figs would be 670 Joules



6.) When 45 g of an alloy is dropped into 100g of water at 25 c the final temp is 37 c. What is the specific heat of the alloy?
I am going to assume that the alloy had been preheated to 100 C before it was dropped in to cold water, in which case the metal dropped from 100 C to 37 C = 63 C drop in temp

find heat given to the water:
dH = m C dT
dH = 100 g (4.184 J/g-C)(12 C rise in temp)
dH = 5021 Joules

find specific heat of the metal:
(5021 Joules ) / (45 g) (63 C drop) = 1.77 J/g-C

but use the drop intemp you were given




7.) By what quantity must the heat capacity of an object be divided to obtain the specific heat of that material ?
a.) mass