review for Energy and Gases

How much heat is required to change 25.8 g of water from 35°C to 98°C? Specific heat of water is 4.18 J/g °C.

• 6780 J

• 4500 J

• 9000 J

• 12000 J

Answer explanation

To find the heat required, use the formula Q = mcΔT. Here, m = 25.8 g, c = 4.18 J/g°C, and ΔT = 98°C - 35°C = 63°C. Thus, Q = 25.8 g * 4.18 J/g°C * 63°C = 6780 J. Therefore, the correct answer is 6780 J.

What is the term for the transition of a material from a gas to a solid?

• Deposition

• Sublimation

• Condensation

• Melting

Answer explanation

The transition of a material from a gas to a solid is called deposition. This process occurs without passing through the liquid phase, unlike condensation, which is the transition from gas to liquid.

Which states exist at the triple point of a substance?

• Solid, liquid, and gas

• Solid and plasma

• Liquid and plasma

• Gas and plasma

Answer explanation

At the triple point of a substance, all three phases—solid, liquid, and gas—coexist in equilibrium. This is a unique condition where temperature and pressure allow these states to exist simultaneously.

Substance A has a specific heat of 0.25 J/g°C, and substance B has a specific heat of 0.68 J/g°C. If both are initially at 25°C, when heated evenly, which will reach 50°C first?

• Substance A

• Substance B

• Both will reach at the same time

• Neither will reach 50°C

Answer explanation

Substance A has a lower specific heat (0.25 J/g°C) compared to substance B (0.68 J/g°C). This means substance A requires less energy to increase its temperature, allowing it to reach 50°C first.

How many calories are in a Big Mac if Fat=9g, Carbohydrates=46 g, and protein=25 g?

Answer explanation

To calculate calories, use the formula: (Fat g x 9) + (Carbohydrates g x 4) + (Protein g x 4). For 9g fat, 46g carbs, and 25g protein, the total is 554 calories. However, the correct answer is 0, indicating a misunderstanding in the question.

If someone ate a doughnut that contained 500 calories, how many hours would they have to exercise to use those calories if they were burning 125 calories per hour?

• 4 hours

• 2 hours

• 6 hours

• 8 hours

Answer explanation

To burn 500 calories at a rate of 125 calories per hour, divide 500 by 125. This gives 4 hours of exercise needed to use the calories from the doughnut.

A student mixed aluminum with hydrochloric acid and the temperature of the surrounding water increased by 25°C. Was the reaction endothermic or exothermic?

Answer explanation

The temperature increase indicates that heat was released during the reaction. Since the surroundings gained heat, the reaction is exothermic.

If a system has a pressure of 2.5 atm and a volume of 1.0 L, what is the new volume if the pressure increases to 7.5 atm?

• 0.33 L

• 0.75 L

• 1.5 L

• 3.0 L

Answer explanation

Using Boyle's Law (P1V1 = P2V2), we can calculate the new volume. With P1 = 2.5 atm, V1 = 1.0 L, and P2 = 7.5 atm, we find V2 = (P1V1)/P2 = (2.5 * 1.0) / 7.5 = 0.33 L. Thus, the new volume is 0.33 L.

How many moles are in a 2.5 L container if the pressure is 1.3 atm and the temperature is 298 K?

• 0.13 moles

• 0.25 moles

• 0.50 moles

• 1.00 moles

Answer explanation

Using the ideal gas law, PV = nRT, we can rearrange to find n (moles): n = PV / RT. Substituting P = 1.3 atm, V = 2.5 L, R = 0.0821 L·atm/(K·mol), and T = 298 K gives n = 0.13 moles, which is the correct answer.

What is the total pressure if a 5.0L container at a temperature of 425K contains 1.3 moles of oxygen and 2.6 moles of nitrogen?

• 16.4 atm

• 8.2 atm

• 24.6 atm

• 4.1 atm

Answer explanation

Using the ideal gas law, PV = nRT, we calculate total pressure. P = (nRT)/V. Here, n = 1.3 + 2.6 = 3.9 moles, R = 0.0821 L·atm/(K·mol), V = 5.0 L, T = 425 K. This gives P = 16.4 atm, the correct answer.