A cup of tea has a mass of 140 grams. Its temperature starts out at T = 40 C. It sits for a while and cools off to room temperature T= 22 C. Answer the next 3 questions about the cup of tea.
1. What is the overall temperature change for the cup of tea?
a. 40 C
b. 22 C
c. 18 C
d. -18 C ****
e. -22 C
2. Is this event consistent with the Law of Conservation of Energy?
a. No. The heat leaves the tea, but this doesn't warm up the room.
b. No. The heat leaves the tea and warms up the room, but doesn't warm up the room enough to measure.
c. Yes. The heat leaves the tea, and the room warms up as much as the tea cools down.
d. Yes. The heat leaves the tea and warms up the room, but doesn't warm up the room enough to measure. *****
Solve for the amount of heat energy in kJ lost by the tea. Recall the specific heat of water is 4.18 joules per gram per degree Celsius. [ 4.18 J/(g C) ]. Report your answer using only 1 digit after the decimal with NO UNITS. (Be sure you calculate your answer in kilojoules (kJ)). *
trick is kJ instead of J
use 4.18 *10^-3 kJ /(g C)
heat lost = 4.18*10^-3 kJ/( g C) * 140 g * 18 C = 10.5
.... and you did the rest right
To find the overall temperature change for the cup of tea, we need to subtract the final temperature from the initial temperature. Therefore, the answer is 40 C - 22 C = 18 C. So the correct option is c) 18 C.
According to the Law of Conservation of Energy, energy cannot be created or destroyed, only transferred or transformed from one form to another. In this case, the heat energy from the tea is transferred to the surroundings, including the room. Therefore, the correct option is d) Yes. The heat leaves the tea and warms up the room, but doesn't warm up the room enough to measure.
To calculate the amount of heat energy lost by the tea, we can use the formula:
Heat Energy (Q) = Mass (m) x Specific Heat Capacity (c) x Temperature Change (ΔT)
Given that the mass of the tea is 140 grams, the specific heat capacity of water is 4.18 J/(g C), and the temperature change is 40 C - 22 C = 18 C, we can calculate the heat energy lost:
Q = 140 g x 4.18 J/(g C) x 18 C = 10533.6 J
To convert the energy from joules to kilojoules, we divide by 1000:
Q = 10533.6 J / 1000 = 10.53 kJ
Therefore, the amount of heat energy lost by the tea is approximately 10.5 kJ.