Question

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

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

Step-by-step solution

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 \((+)\).

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 \((- )\).

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 \( (- )\).

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 \((- )\).

Water evaporating

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

Key concepts

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.