Calculate the quantity of energy needed to heat 8.0 g of water from 42.0 °C to 45.0 °C. Report your answers in scientific notation.

Answer 1

The energy (heat) required to increase the temperature of a substance is proportional to the mass of the substance and the number of degrees the temperature will be increased:

q = mC_sΔT where q = heat (Joules), m = mass (g), C_s = specific heat of substance (water), and

ΔT = change in temperature (°C), ΔT = T_final – T_initial

asked for: q

given: m = 8.0 g

ΔT = 45.0°C – 42.0°C

look up C_s for water: 4.18 ^J/_(g•°C)

Substitute the values into the equation and solve for q.

Answer 2

q = mCΔT

q = heat = ?

m = mass = 8.0 g

C =specific heat of water = 4.184 J/g/deg

ΔT = change in temperature = 3.0 degrees

q = (8.0 g)(4.184 J/g/deg)(3.0 deg) = 100.4 J

Because the temperature increased, the sign will be negative

Answer = -1.0x10² J