To find the initial temperature of glass

Question

When 0.2 kg of coffee at 80°C is poured into 0.45 kg glass,the final temperature of coffee is 65°C.If no heat is gained or lost from the outside,what is the initial temperature of glass? Assume that the specific heat capacity of coffee is 4200JkgK and that of glass is 800JkgK.

Answer 1

cp = q/mΔT

We know that the two q's are equal because the Joules that left the coffee entered the glass until equilibrium is reached.

So, q = (cp)m(ΔT)

(cp of coffee)( mass of coffee)(ΔT coffee) = (cp of glass)( mass of glass)(ΔT glass)

(4200J/kgK)(.2 kg)(65 - 80) = (800J/kgK)(.45 kg)(65 - Ti)

Solve for Ti. Ignore K vs C; they are the same when measuring a delta (change in).