Calculate the value of q for each of the experiments listed below. (Assume the heat capacity of water is 4.1801 J/g*C).

Exp1: 2.48g of an unknown salt added to 160. mL of water resulted in a change of temperature of -0.1 C.

Exp2: 2.48g of an unknown salt added to 160. mL of water resulted in a change of temperature of 0.7 C.

Exp3: 2.48g of an unknown salt added to 160. mL of water resulted in a change of temperature of -1.8 C.

salt + H2O ==> solution - heat or

salt + H2O + heat ==> solution. endothermic for #1 and #3. Exothermic for #2. Therefore, for the salt, q is + for 1 and 3 and - for #2.
Do you want q/g? You don't have the molar mass so you can't get q/mol.
qH2O = mass H2O x specific heat H2O x delta T
qH2O = 160 x 4.1801 x 0.1 = about 66.9 J/2.48g = about 27 J/g.

The others are done the same way.

Why did you use 160 instead of 2.48 g ?

and , how do I know #1 and #3 is endothermic and #2 is exothermic ?
thank you

You use the water as a way of knowing how much heat was lost or gained. So the salt changed T from zero c to -1.0 C. Since it cooled the water you know the reaction is endothermic; i.e. it took heat away from the water so the rxn required heat and that is endothermic. Rxns that cause an increase in T means it is giving off heat and that is exothermic.

For #1, the heat taken away from the water is measured by the water.
mass H2O x specific heat H2O x delta T.
The mass H2O = 160g
sp.h. H2O is 4.18 J/g*C
and delta T is 0.1C.
So that gives you q for the 2.48g of the salt that was dropped into the water. q/2.48 = J/gram.

To calculate the value of q for each experiment, we can use the equation:

q = m * C * ΔT

where q is the heat absorbed or released by the system, m is the mass of the substance being heated or cooled, C is the specific heat capacity of the substance, and ΔT is the change in temperature.

For all three experiments, the mass of the substance (unknown salt) is given as 2.48g, and the specific heat capacity of water is given as 4.1801 J/g*C.

Let's calculate the value of q for each experiment:

Exp1:
m = 2.48g
C = 4.1801 J/g*C
ΔT = -0.1 C

q = 2.48g * 4.1801 J/g*C * (-0.1 C)
= -1.032968 J

Therefore, the value of q for Experiment 1 is approximately -1.032968 J.

Exp2:
m = 2.48g
C = 4.1801 J/g*C
ΔT = 0.7 C

q = 2.48g * 4.1801 J/g*C * 0.7 C
= 7.349904 J

Therefore, the value of q for Experiment 2 is approximately 7.349904 J.

Exp3:
m = 2.48g
C = 4.1801 J/g*C
ΔT = -1.8 C

q = 2.48g * 4.1801 J/g*C * (-1.8 C)
= -17.785568 J

Therefore, the value of q for Experiment 3 is approximately -17.785568 J.

Hope this helps!