Calorimetry Aim: To calculate the change in energy during an exothermic or endothermic reaction.
Measuring Heat Energy Heat is measured in Joules or kilojoules English unit is Calories 1 Cal= 1 kilocalorie= 4.18 joules
Calorimeter an insulated device used to measure the absorption or release of heat in water.
Calculating Heat
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= Tf-Ti 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.
If 50.0 g of water and 50.0 g of copper each absorb 2500. joules of energy, which substance will have the greater increase in temperature? Specific heat= 4.18 J/g C Specific heat= 0.386 J/g C Which substance had the greater increase in temperature? Explain why using specific heat capacity.
A chef can use an iron or copper skillet to heat oil for cooking. The following information is known about each skillet: Mass= 150.0 grams Specific heat= 0.450 J/g C On medium heat,it s temperature increases by 15 C in 2 minutes. Mass= 150.0 grams Specific heat= 0.386 J/g C On medium heat, it s temperature increases by 25 C in 2 minutes. Which pan is better at heating and WHY?
Heat Calculations Example #1 If 45.75 g of water changes temperature from 36.0 C to 79.0 C, how much energy did this require?
Heat Calculations Example #2 Determine the quantity of aluminum that loses 13450. joules to decrease its temperature by 59.8 C? The specific heat capacity of aluminum is 0.900 J/g C
Heat Calculations Example #3 If 26.7 grams of water at 87.0 C releases 15850. J of energy, what is the final temperature?
Heat Calculations Example #4 Determine the initial temperature of a 16.0 g sample of water at 35.8 C that absorbed 5675 J of energy?
Example #5 Calculating Heat 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.
Practice 1. How many joules of heat are given off when 5.0 g of water cools from 75 C to 25 C? 2. When 20 grams of water is cooled from 20 C to 10 C, the number of joules of heat released is?
Practice 3. 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 C to 30 C? 4. How many joules of heat are needed to raise the temperature of a 4.0 gram sample of water 8.0 celsius degrees?
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)
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?
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
Heat flow Heat flows from hot to cold until both objects reach the same temperature The heat lost by one object is equal to the amount of heat gained by another object
Heat transfer: metal and water
Example #5- Solving for the specific heat of a metal 100.00 grams of water at 22.4 C is placed in a calorimeter. A heated 75.25 gram sample of Al 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. Calculate the specific heat of the aluminum.
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?