Explanation:
The key to this problem lies in the value of the specific heat of iron.
ciron=0.108 cal g−1∘C−1
This tells you that in order to increase the temperature of one unit of mass of iron, i.e. of 1 g of iron, by one unit of temperature, i.e. by 1∘C, you need to provide it with 0.108 cal.
Now, you can use the specific heat of iron to figure out the amount of heat needed to increase the temperature of 35.0 g of iron
35.0g⋅0.108 cal1g⋅1∘C=3.78 cal ∘C−1
This tells you that in order to increase the temperature of 35.0 g of iron by 1∘C, you need to provide it with 3.78 cal of heat.
In your case, the temperature of the iron must increase by
35∘C−25∘C=10∘C
which means that you will need
10∘C⋅3.78 cal1∘C=37.8 cal
Now, you should round the answer to one significant figure, the number of sig figs you have for the change in temperature, i.e. for 10∘C, but I'll leave it rounded to two sig figs
heat needed = 38 cal−−−−−−−−−−−−−−−−−−
