Calorimetry. Aim: Calculating the energy change during a reaction.

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1 Calorimetry Aim: Calculating the energy change during a reaction.

2 Measuring Heat Energy Heat is measured in Joules or kilojoules

3 Calorimeter an insulated device used to measure the absorption or release of heat in water.

4 Calculating Heat

5 Calculating Heat To calculate the energy absorbed or released we use the formula: Q=mcΔT Q= heat. Measured in Joules ΔT= change in temperature in C or K. m= mass in grams. ΔT= T final -T initial C= specific heat capacity** Found in Table B for water. Specific heat capacity: the amount of energy required to raise the temperature 1 g of a substance by 1 C or 1 K. **The greater the specific heat, the longer it takes a substance to heat up or cool down.**

6 Calculating Heat 1. How many joules of heat are given off when 5.00 g of water cools from C to C?

7 Calculating Heat 5. The temperature of a sample of water in the liquid phase is changed from 15.0 C to 25.0 C by the addition of 840. joules. What is the mass of the water?

8 Calculating Heat 7. The temperature of 50. grams of water was raised to 50. C by the addition of Joules of heat energy. What was the initial temperature of the water?

9 1) a. If 50.0 g of water and 50.0 g of copper each absorb joules of energy, which substance will have the greater increase in temperature? Specific heat= 4.18 J/g C Specific heat= J/g C b.) Which substance had the greater increase in temperature? Explain why using specific heat capacity.

10 Heat Calculations 2) If g of water changes temperature from 36.0 C to 79.0 C, how much energy did this require?

11 Heat Calculations 3) Determine the quantity of aluminum that loses joules to decrease its temperature by 59.8 C? The specific heat capacity of aluminum is J/g C

12 Heat Calculations 4) If 26.7 grams of water at 87.0 C releases 1585 J of energy, what is the final temperature?

13 Heat Calculations 5) Determine the initial temperature of a 16.0 g sample of water at 35.8 C that absorbed 5675 J of energy?

14 Calculating Heat 6) If 16.7 grams of ethanol cools from 100. C to 82 C by releasing 739 J of energy, determine the specific heat capacity of the ethanol.

15 Practice 7. How many joules of heat are given off when 5.0 g of water cools from 75.0 C to 25.0 C? 8. When 20 grams of water is cooled from 20.0 C to 10.0 C, the number of joules of heat released is?

16 Practice 9. What is the total number of joules of heat that must be absorbed to change the temperature of 100. grams of H 2 O from 25.0 C to 30.0 C? 10.How many joules of heat are needed to raise the temperature of a 4.0 gram sample of water 8.5 C?

17 Practice 5. The temperature of a sample of water in the liquid phase is changed from 15 C to 25 C by the addition of 840 joules. What is the mass of the water? 6. How many joules of heat are required to raise the temperature of 20 gams of methanol from 30 C to 40 C? (Specific heat of methanol= 6.5 j/g C)

18 Practice 7. The temperature of 50 grams of water was raised to 50 C by the addition of 1,050 joules of heat energy. What was the initial temperature of the water? 8. How many kilojoules are equivalent to 10 joules?

19 Practice 9. The temperature of 100 grams of water changes from 16 C to 20 C. What is the total number of joules of heat energy absorbed by the water? 10. The greatest amount of heat energy would be required to raise the temperature of a 1 gram sample of water from? a) 10 C to 30 C c) 20 C to 30 C b) 30 C to 60 C d) 40 C to 60 C

20 Conservation of Energy Aim: The complete energy calculations utilizing the first law of thermodynamics.

21 Conservation of Energy Thermal energy will flow between objects with a different temperature. All energy that flows from a system into a surroundings and vice versa is conserved. Therefore, the heat lost by one substance is equal to the amount of heat gained by another object Q lost = Q gained

22 Example #5- Solving for the specific heat of a metal grams of water at 22.4 C is placed in a calorimeter. A heated gram sample of metal at a temperature of 99.3 C is placed into the calorimeter with the water. Heat is transferred until the both objects reach a final temperature of 32.9 C. Determine the specific heat of the metal.

23 Example #6- Solving for the specific heat of a metal A 25 gram sample of a metal at 75.0 C is placed in a calorimeter containing 25g of water at 20.0 C. The temperature stops changing at 29.4 C. What is the specific heat of the metal?