►ThermochemistryThermochemistry - concerned - concerned with heat changes that occur with heat changes that occur during chemical reactionsduring chemical reactions

Heat, qHeat, q

energy that transfers from one object energy that transfers from one object

to another, because of a temperature to another, because of a temperature

difference between themdifference between them

Energy that flows from something Energy that flows from something

warmerwarmer to something to something coolercooler

Learning CheckLearning Check

A. When you touch ice, heat is transferredA. When you touch ice, heat is transferred

fromfrom

1) your hand to the ice1) your hand to the ice

2) the ice to your hand2) the ice to your hand B. When you drink a hot cup of coffee, heatB. When you drink a hot cup of coffee, heat

is transferred fromis transferred from

1) your mouth to the coffee1) your mouth to the coffee

2) the coffee to your mouth2) the coffee to your mouth

Learning CheckLearning Check

When you heat 200 g of water for 1 minute, the When you heat 200 g of water for 1 minute, the water temperature rises from 10°C to 18°C. water temperature rises from 10°C to 18°C.

If you heat 400 g of water at 10°C in the same If you heat 400 g of water at 10°C in the same pan with the same amount of heat for 1 pan with the same amount of heat for 1 minute, what would you expect the final minute, what would you expect the final temperature to be?temperature to be?

1) 10 °C1) 10 °C 2) 14°C 2) 14°C 3) 18°C3) 18°C

200 g400 g

SolutionSolution

2)14°C2)14°C

Heating twice the mass of water using the Heating twice the mass of water using the same amount of heat will raise the same amount of heat will raise the temperature only half as much.temperature only half as much.

200 g400 g

Some Equalities for HeatSome Equalities for Heat

Heat is measured in calories or joules

• 1 kcal = 1000 calorie

• 1 Calorie = 1000 calorie

• 1 calorie = 4.18 J

• 1 kJ = 1000 J

Specific Heat CapacitySpecific Heat Capacity

Why do some foods stay hot longer than Why do some foods stay hot longer than

others?others?

Why is the beach sand hot, but the water is Why is the beach sand hot, but the water is

cool on the same hot day?cool on the same hot day?

Specific Heat CapacitySpecific Heat Capacity

the amount of heat energy needed to raise the temperature of 1 g of a the amount of heat energy needed to raise the temperature of 1 g of a substance by 1°Csubstance by 1°C

cal/g-°Ccal/g-°C

water water 1.00 1.00 aluminumaluminum 0.220.22

coppercopper 0.0930.093

Substances with low specific heat capacities requires Substances with low specific heat capacities requires ________ (more or (more or less?)less?) energy to feel hot than those with high specific heat capacities energy to feel hot than those with high specific heat capacities

At the same mass and amount of heat added, substances with low specific At the same mass and amount of heat added, substances with low specific heat capacities will be heat capacities will be ________ (hotter or cooler?)(hotter or cooler?) than those with high than those with high specific heat capacitiesspecific heat capacities

lessless

Time (min)Time (min) 11 22 33 1111

Heat Heat added (cal)added (cal)

0.0930.093 0.1860.186 0.2790.279 1.0231.023

Water Water

C =1.00 C =1.00 cal/g-cal/g-ooCC

AluminumAluminum

C =0.22 C =0.22 cal/g-cal/g-ooCC

CopperCopper

C =0.093 C =0.093 cal/g-cal/g-ooCC

26 26 ooC C

26 26 ooC C

26 26 ooC C 29 29 ooC C

36 36 ooC C

Specific Heat CapacitySpecific Heat Capacity

At the same mass and amount of heat, At the same mass and amount of heat, substances with low specific heat capacities substances with low specific heat capacities will be will be ________ (hotter or cooler?)(hotter or cooler?) than than those with high specific heat capacitiesthose with high specific heat capacities

hotterhotter

11

Water has a HUGE value, compared to other chemicals

For water, C = 4.18 J/(g oC), and also C = 1.00 cal/(g oC)

Thus, for water:• it takes a long time to heat up, and• it takes a long time to cool off!

Water is used as a coolant!

Learning Check

A. A substance with a large specific heat capacity 1) heats up quickly 2) heats up slowly

B. When ocean water cools, the surrounding air 1) cools 2) warms 3) stays the same

C. Sand in the desert is hot in the day, and cool at night. Sand must have a

1) high specific heat capacity 2) low specific heat capacity

Calculating Calculating Heat, qHeat, q

mass x temp. change x specific heat capacitymass x temp. change x specific heat capacity

m x m x T x T x CC

Molar heat capacity, Molar heat capacity, ΔΔHH

Amount of heat energy required to Amount of heat energy required to increase the temperature of increase the temperature of one moleone mole of a of a substance by one Kelvinsubstance by one Kelvin

ΔH = CΔTΔH = CΔT

Heat CalculationsHeat Calculations

A hot-water bottle contains 750 mL of A hot-water bottle contains 750 mL of water at 65°C. If the water cools to water at 65°C. If the water cools to body temperature (37°C), how many body temperature (37°C), how many calories of heat could be transferred to calories of heat could be transferred to sore muscles?sore muscles?

heat = m x heat = m x T x Sp. Ht. (HT x Sp. Ht. (H22O)O)

= 750 g x 28°C x = 750 g x 28°C x 1.00 cal 1.00 cal g - °C g - °C

= 21 000= 21 000

Learning CheckLearning Check

How many kcal are needed to raise How many kcal are needed to raise the temperature of 120 g of water the temperature of 120 g of water from 15°C to 75°C?from 15°C to 75°C?

1) 1.8 kcal1) 1.8 kcal

2) 7.2 kcal2) 7.2 kcal

3) 9.0 kcal3) 9.0 kcal

SolutionSolution

How many kcal are needed to raise the temperature of 120 g of water from 15°C to 75°C?

2) 7.2 kcal

120 g x (75°C - 15°C) x 1.00 cal x 1 kcal

g - °C 1000 cal

CalorimeterCalorimeter

• a device used to measure heat energy

• can be used to measure the specific heat capacity of materials by measuring the water’s temperature change as a warm object is placed in the calorimeter

Energy and NutritionEnergy and Nutrition

a Calorie, written with a capital C, always refers to the energy in food

1 Calorie (nutritional) = 1 kcal

1 Cal = 1000 cal

Caloric Food ValuesCaloric Food Values

Carbohydrate = 4 kcal/g

Fat = 9 kcal/g

Protein = 4 kcal/g

Foods and CaloriesFoods and Calories

Food Carbo Fat Protein Energy(kcal)

carrots, 1 cup 11g 0g 1g 48

banana 26 0 1 108

egg 0 6 6 78

beef (3 oz) 0 5 22 133

Learning Check Learning Check

1.0 cup of whole milk contains 12 1.0 cup of whole milk contains 12 g of carbohydrate, 9.0 g of fat, g of carbohydrate, 9.0 g of fat, and 9.0 g of protein. How many and 9.0 g of protein. How many kcal (Cal) are obtained?kcal (Cal) are obtained?

1) 48 kcal1) 48 kcal

2) 81 kcal2) 81 kcal

3) 165 kcal3) 165 kcal

Solution Solution

3) 165 kcal

12 g carbo x 4 kcal/g = 48 kcal

9.0 g fat x 9 kcal/g = 81 kcal

9.0 g protein x 4 kcal/g = 36 kcal

Total kcal = 165 kcal