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Chapter 4: Problem 14

Indicate with a plus sign \((+)\) any of these processes that require energy and a negative sign \((-)\) any that release energy. (a) riding a bike (d) tires deflating (b) fireworks bursting (e) wood burning in a fireplace (c) water evaporating

Short Answer

Expert verified
(a) +, (d) -, (b) -, (e) -, (c) +

Step by step solution

01

Riding a bike

Riding a bike requires energy because it involves pedaling and using muscular power to propel the bike forward. Hence, this process requires an input of energy. Mark with a plus sign \((+)\).
02

Tires deflating

Deflating tires means air is escaping from the tires. This process naturally releases energy with the escape of compressed air. Mark with a negative sign \((- )\).
03

Fireworks bursting

When fireworks burst, they release energy in the form of light, sound, and heat. Such an explosive reaction signifies the release of stored chemical energy. Mark with a negative sign \( (- )\).
04

Wood burning in a fireplace

Burning wood in a fireplace releases energy in the form of heat and light through the combustion process. This is an exothermic reaction. Mark with a negative sign \((- )\).
05

Water evaporating

Evaporation involves water molecules absorbing energy to transition from liquid to gas. This process requires energy input. Mark with a plus sign \((+)\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Understanding Endothermic Processes
Endothermic processes absorb energy from their surroundings. These types of processes require an input of energy. A clear example is water evaporating. Here, water molecules need to absorb heat from the environment to change from a liquid to a gas state. This absorption of heat is why it feels cooler around evaporating water. When water evaporates, it is transitioning from a low-energy state (liquid) to a higher-energy state (gas). Riding a bike is also endothermic because it needs energy input from your muscles to move the pedals and propel the bike forward.
  • Endothermic processes take in energy.
  • Examples include water evaporating and riding a bike.
  • They usually feel cooler or require physical work.
Understanding Exothermic Reactions
Exothermic reactions release energy into their surroundings. These reactions usually give off heat, light, or sound. A classic example is wood burning in a fireplace. When wood burns, it undergoes combustion, releasing a significant amount of heat and light. Fireworks bursting is another example where stored chemical energy in the firework compound is released explosively as light, sound, and heat. Similarly, when tires deflate, the compressed air escapes, releasing energy in the process.
  • Exothermic reactions release energy.
  • Examples include burning wood and fireworks bursting.
  • These processes often produce light, heat, or sound.
Energy Transfer in Reactions
In any chemical reaction or physical process, energy is either absorbed or released. Endothermic processes absorb energy, while exothermic reactions release energy. This transfer of energy is a fundamental aspect of how reactions occur and proceed. For instance, when you ride a bike, your body transfers energy to the bike through your muscles. In contrast, burning wood in a fireplace energy is transferred to the surroundings as heat and light.

Understanding these energy flows helps us make sense of everyday phenomena and chemical reactions. By identifying whether a process requires or releases energy, we can predict the behavior of reactions and their effects on their environment.

  • Energy is either absorbed or released in reactions.
  • Energy transfer is crucial to understanding reaction behaviors.
  • It helps predict effects on the environment.

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Most popular questions from this chapter

Suppose a ball is sitting at the top of a hill. At this point, the ball has potential energy. The ball rolls down the hill, so the potential energy is converted into kinetic energy. When the ball reaches the bottom of the hill, it goes halfway up the hill on the other side and stops. If energy is supposed to be conserved, then why doesn't the ball go up the other hill to the same level as it started from?

If you are boiling some potatoes in a pot of water, will they cook faster if the water is boiling vigorously than if the water is only gently boiling? Explain your reasoning.

Gloves are often worn to protect the hands from being burned when they come in contact with very hot or very cold objects. Gloves are often made of cotton or wool, but many of the newer heat-resistant gloves are made of silicon rubber. The specific heats of these materials are listed below: $$ \begin{array}{|l|c|} \hline \text { Material } & \text { Specific heat }\left(\mathbf{J} / \mathrm{g}^{\circ} \mathbf{C}\right) \\ \hline \text { wool felt } & 1.38 \\ \hline \text { cotton } & 1.33 \\ \hline \text { paper } & 1.33 \\ \hline \text { rubber } & 3.65 \\ \hline \text { silicon rubber } & 1.46 \\ \hline \end{array} $$ (a) If a glove with a mass of \(99.3\) grams composed of cotton increases in temperature by \(15.3^{\circ} \mathrm{F}\), how much energy was absorbed by the glove? (b) A glove with a mass of \(86.2\) grams increases in temperature by \(25.9^{\circ} \mathrm{F}\) when it absorbs \(1.71 \mathrm{~kJ}\) of energy. Calculate the specific heat of the glove and predict its composition. (c) If a glove with a mass of \(50.0\) grams needs to absorb \(1.65 \mathrm{~kJ}\) of energy, how much will the temperature of the glove increase for each of the materials listed above? (d) Which is the best material for a heat-resistant glove? (e) If you were designing a heat-resistant glove, what kind of specific heat would you look for?

Homogenized whole milk contains \(4 \%\) butterfat by volume. How many milliliters of fat are there in a glass \((250 \mathrm{~mL})\) of milk? How many grams of butterfat \((d=0.8 \mathrm{~g} / \mathrm{m} \mathrm{L})\) are in this glass of milk?

Suppose \(25 \mathrm{~g}\) of solid sulfur and \(35 \mathrm{~g}\) of oxygen gas are placed in a sealed container. (a) Does the container hold a mixture or a compound? (b) After heating, the container was weighed. From a comparison of the total mass before heating to the total mass after heating, can you tell whether a reaction took place? Explain. (c) After the container is heated, all the contents are gaseous. Has the density of the container including its contents changed? Explain.
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