Homework:

Page 498, problems 12-13

Page 500, questions 15-19

12.If 335g of water at 65.5oC loses 9750J of heat, what is the final temperature of the water?

12.If 335g of water at 65.5oC loses 9750J of heat, what is the final temperature of the water?

q = cm∆T

12.If 335g of water at 65.5oC loses 9750J of heat, what is the final temperature of the water?

q = cm∆T ∆T = q / cm

12.If 335g of water at 65.5oC loses 9750J of heat, what is the final temperature of the water?

q = cm∆T ∆T = q / cm = 9750J / (4.184J/go)(335g)

12.If 335g of water at 65.5oC loses 9750J of heat, what is the final temperature of the water?

q = cm∆T ∆T = q / cm = 9750J / (4.184J/go)(335g) = 7oC

12.If 335g of water at 65.5oC loses 9750J of heat, what is the final temperature of the water?

q = cm∆T ∆T = q / cm = 9750J / (4.184J/go)(335g) = 7oC 65.5 – 7 = 58.5oC

13.The temperature of a sample of water increases from 20.0oC to 46.6oC as it absorbs 5650J of heat. What is the mass of the sample?

13.The temperature of a sample of water increases from 20.0oC to 46.6oC as it absorbs 5650J of heat. What is the mass of the sample?

q = cm∆T

13.The temperature of a sample of water increases from 20.0oC to 46.6oC as it absorbs 5650J of heat. What is the mass of the sample?

q = cm∆T

m = q / c∆T

13.The temperature of a sample of water increases from 20.0oC to 46.6oC as it absorbs 5650J of heat. What is the mass of the sample?

q = cm∆T

m = q / c∆T = 5650J / (4.184J/go)(26.6o)

13.The temperature of a sample of water increases from 20.0oC to 46.6oC as it absorbs 5650J of heat. What is the mass of the sample?

q = cm∆T

m = q / c∆T = 5650J / (4.184J/go)(26.6o) = 50.8g

15.Why does ∆H for an exothermic reaction have a negative value?

15.Why does ∆H for an exothermic reaction have a negative value?

The reaction gives off heat, so the products have less heat than the reactants did. The change is negative.

16.Why is a measured amount of water an essential part of a calorimeter?

16.Why is a measured amount of water an essential part of a calorimeter?

q = cm∆Tc = 4.184 J/go

17.Explain the meaning of ∆Hrxn. Why is ∆Hrxn sometimes positive and sometimes negative?

17.Explain the meaning of ∆Hrxn. Why is ∆Hrxn sometimes positive and sometimes negative?

Positive for endothermic reactions

Negative for exothermic reactions.

18.Could another liquid be used just as effectively as water in a calorimeter? Why or why not?

18.Could another liquid be used just as effectively as water in a calorimeter? Why or why not?

q = cm∆Tc = _____ J/go

19.Explain how you would design and experiment to determine the specific heat of a 45g piece of metal.