The specific heat capacity of rubidium is 0.360 j/g°c. a sample of rubidium absorbs 40.0 kj
when heated from 12.5 °c to 38.0 °c. calculate the mass of the rubidium sample.

4.36 kg rubidium.

That is; Q = mcΔT

We are given;

Quantity of heat = 40.0 kJ or 40,000 Joules

Mass of rubidium = 0.360 J/g°C

Change in temperature, ΔT = 38.0°C - 12.5°C

                                              = 25.5°C

We are required to calculate the mass of rubidium

From the formula;Q = mcΔT

mass = Q ÷ cΔT

        = 40,000 ÷(0.360 J/g°C× 25.5°C)

        = 4,357.30 g

       = 4.36 kg

Therefore, the mass of 4.36 kg rubidium.

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.