Heat Quiz

How does the potential-energy diagram for a reaction indicate whether the reaction is endothermic or exothermic?

An endothermic reaction has reactants that are lower in energy than products because energy is absorbed to form the products.

Which statement about exothermic reactions is accurate?

As reactants form products, the potential energy decreases.

Which reaction is exothermic?

CH4 + 2O2 --> CO2 + 2H2O + 891 kJ

The diagram below shows the temperature dropping from 80°C to 20°C. Molecules that have longer arrows are moving faster. Which statement describes what is happening in this system?

Kinetic energy decreases as temperature decreases.

A student touches a freshly baked cake that was taken out of the oven. Which best explains why the cake feels hot?

Molecules in the cake are moving faster than molecules in the skin.

Two samples of carbon come into contact. A heat transfer will occur between sample A and sample B. What must be true for heat to transfer from sample A to sample B?

The average kinetic energy of A is greater than that of B.

Two different gases are stored in separate closed containers. If both gases have a temperature of 50°C, which statement is true?

The gas molecules in both containers have the same average kinetic energy.

Iron reacts with oxygen in a chemical hand-warmer. How should this reaction be categorized?

as an exothermic process because it releases heat

In what type of reaction or process does heat flow into the system?

endothermic

What is thermal energy?

the kinetic energy of particles in a system