Question

You may have had a cup of hot coffee at breakfast this morning. Assume you drank 240 mL of coffee at 80 C and that this amount was cooled by your body to the normal 37 C. How many calories were supplied to your body? Assume that the coffee is essentially hot water with a density of 1.0g/mL.

Answer 1

Obtain the specific heat capacity of water

C = 4.184 J / g deg C

Convert volume of water into g using density

Mass of water

=145 mL x 1 g / 1 mL

= 145 g

Use equation of heat exchange

q = m C delta T

here m is the mass of the water, q is the heat exchanged, C is specific heat of water.

Delta T is the change in T

Plugin the values

q= 145 g x 4.184 J / g deg C x ( 37 – 80) deg C

= -43178.9 J

Convert this value using

1 Cal = 4.184 J

q = -43178.9 J x 1 cal / 4.184 J

q = -10320 cal

minus sign shows that heat is given out by water and that is taken by body

So heat taken by body = 10320 Cal