Heat

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.

Heat that flows by conduction is the transfer of thermal energy between substances in contact. What must occur for this to happen?

One system must have higher kinetic energy than the other system.

The temperature of a gas is increased. Which statement best explains the effect that this has on the motion of gas particles?

The average kinetic energy increases, and the particles collide more frequently.

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.

Which answer defines exothermic reaction?

a process in which energy is released as heat

What is thermal energy?

the kinetic energy of particles in a system

Which event is endothermic?

the melting of ice