HN Chemistry LAP 11 Study Guide

What is chemical potential energy?

energy stored in the chemical bonds of a substance

What is true about heat energy?

• It is energy that transfers between objects because of a temperature difference between them

• if two objects remain in contact, heat will continue to flow until the temperature of both objects is the same

• Heat is represented by the letter q in thermochemistry

The Law of Conservation of Energy

states that in any chemical or physical process energy is neither created or destroyed

The system releases heat to the surroundings.

Exothermic

A person (the system) sits next to a hot campfire.

Endothermic

Hot melted wax (the system) solidifies as it cools.

Exothermic

Ammonium nitrate (the system) dissolves and the cold pack becomes cold.

Endothermic

An icicle (the system) melts into liquid water.

Endothermic

Water vapor (the system) condenses into liquid water.

Exothermic

What is the biggest difference between an exothermic and endothermic process?

The direction of energy flow

What occurs in ammonium nitrate cold packs, what statements are true?

• More energy is required (absorbed) to break the solid ionic compound apart

• More energy is absorbed than released in the dissolving process

• bonds broken are stronger

What occurs in calcium chloride hot packs, what statements are true?

• less energy is required (absorbed) to break the solid ionic compound apart

• more energy is released than absorbed in the dissolving process

• bonds formed are stronger

#13-16 on Study Guide

What are examples of water's high specific heat capacity? Because of water's high specific heat capacity

• Temperatures are more moderate in cities found along the coast, near the ocean

• Farmers can protect their fruit trees from frost damage by spraying them with water before a freeze

• Car engines are cooled using coolant, which is comprised of water and ethylene glycol

Which of the following objects has a greater heat capacity? 2 kg iron frying pan OR 2 g iron nail

A 2 kg iron frying pan

Which of the following objects has a greater heat capacity? 20 kg puddle OR 20 kg iron sewer cover

A 20 kg puddle

specific heat capacity

The amount of heat it takes to raise the temperature of 1 gram of a substance 1 degree Celsius

#21-23 on Study Guide

The temperature of a 95.0 gram piece of copper increases from 25.0°C to 48.0°C when the copper absorbs 849 Joules of heat. What is the specific heat of copper?

0.39 J/(g x °C)

How much heat, in Joules, is required to raise the temperature of 80.0 grams of aluminum from 20°C to 75°C?

3960 J

How much heat, in calories, is required to raise the temperature of 250.0 g of mercury by 52°C?

429 calories

A 26.3 g sample of an unknown substance was heated from 22.1°C to 34°C. In the process, the substance absorbed 74 Joules of energy. What is the specific heat of the substance?

0.24 J/(g x°C)

#28 on Study Guide

What is true about a calorimeter?

• The container is insulated so that all of the heat energy is transferred into or out of the water it contains

• uses water to measure the enthalpy change of the system

• Nutritionists use a bomb calorimeter to determine the number of calories released by food

In the Cold Pack Lab, you added ammonium nitrate (the system) to water (the surroundings). You then measured the amount of heat ____

lost by the water as it was absorbed by the ammonium nitrate dissolving process

100 grams of ammonium chloride, NH4Cl, was placed in a foam cup calorimeter containing 124.0 mL of water at 20.0°C. The water temperature decreased to -5°C. Calculate how much heat, in Joules, was absorbed in the dissolving process.

12958 J

When 50 mL of water containing 0.25 mol NaOH at 21.0°C is mixed with 50 mL of water containing 0.25 mol HCl at 21.0°C in a calorimeter, the temperature of the solution increases to 30°C. What is the enthalpy change in kilojoules (kj)?

-3.76 kJ

A potato chip is placed in a bomb calorimeter containing 250 mL of water at 20.0°C. The water reaches a maximum temperature of 55.0°C. How many calories of heat were released by the chip?

-8750 calories

How many dietary (food) calories are in the potato chip in the previous question? (round to whole number)

9 Calories

In the following thermochemical equation, CaO(s) + H2O(l) → Ca(OH)2(s) + 65.2 kJ. What happened?

65.2 kJ of heat are produced by the reaction of CaO and H2O

What would be the correct heat of reaction equation for the preceding reaction?

CaO(s) + H2O(l) Ca(OH)2(s) AH = -65.2 kJ

#37 on Study Guide

CaO(s) + H2O(l) Ca(OH)2(s) + 65.2 kJ

If 3.6 moles of CaO(s) react with water, how much heat is involved?

234.7 kJ

What would be the correct thermochemical equation to describe the following reaction: 2 moles of liquid hydrogen peroxide (H₂O₂) produce 196.4 kJ of heat when it decomposes into 2 moles of liquid water and one mole of oxygen gas.

2H₂O₂ (I) → 2H₂O (l) + O₂ (g) + 196.4 kJ

In the following reaction 2NaHCO3(s) + 129 kJ → Na2CO3(s) + H2O(g) + CO2(g). What happened?

129 kJ of heat are absorbed by the decomposition of NaHСО3

What is another way to write the thermochemical equation previously?

2NaHCO₃(s) → Na₂CO₃(s) + H₂O(g) + CO₂(g) AH = +129 kJ

#42 on Study Guide

2NaHCO3(s) + 129 kJ Na2CO3(s) + H2O(g) + CO2(g)

If three moles of NaHCO3 are decomposed, how much heat is involved?

193.5 kJ

#44-45 on Study Guide