How much energy is needed to heat enough water to make s cup of tea (250 mL), if the water is initially at 20.0 degrees Celsius and you want to increase the temperature to 85.0 degrees Celsius? (assume that 250mL = 250 g)

Heat energy is given by; Mcθ

where m is the mass, c is the specific heat capacity and θ is the change in temperature;

Mass of water is 250 g, specific heat of water is 4.18 J/g/k, and θ is the change in temperature

thus; heat = 250 * 4.18 * 65

= 67925 Joules or 67.925 kJ

To solve this question you need to know the specific heat of the object, which is water. The specific heat of water is 1 calorie/gram °C = 4.2 joule/gram °C. The energy needed would be:

Q = c * m*ΔT

Q = 1 calorie/gram °C * 250 g * (85-25°C)

Q = 15000 calorie = 63000J