Question

32. Which of the following is a chemical change? A) cutting a rope B) bending a steel rod C) making a snowman D) burning sugar E) melting gold 33. How many calories are required to raise the temperature of a 150. g sample of gold from 25 °C to 175 °C? The specific heat of gold is 0.0308 cal/g °C. Hint: Heat- Mass x specific heat x Temp. change A) 4.62 cal B) 116 cal zamx5. HDT f C) 22500 cal D) 693 cal E) 130 cal 34. One cup of kidney beans contains 15 g of protein, 1 g of fat, and 42 g of carbohydrate. How many kilocalories, to two significant figures, does this sample cutain? The accepted caloric values for foods are 4.0 kcal/g for carbohydrate, 9 kcal/g for fat, an' kul/g for protein.) Report the answer to 2 significant figures. A) 60 kcal B) 88 kcal C) 230 kcal D) 240 kcal E) 520 kcal 35. Given: C3H8 + 5 O2 — 3C02 + 4H2O Heat= -2500 Kjoules How many Kjoules of heat released if 3.00 moles of C3H8 is reacted with oxygen? decays hy heta su A. -2500 Kj B. -5000 Kj C. -1250 Kj D. -7500 Kj E. - 500 Kj

Answer 1

32-

A chemical change is that process where the product undergoing chnage completely chnages into another products and there is no similarities in the physical and chemical properties between the original and the final product.

Here the chemical change process is Burning of sugar i.e

C12H22O11 (sugar) + 12 O2 ------------> 12 CO2(g) + 11 H2O (g)

Here the original compund sugar is a solid and the final products are gases with different chemical and physical properties than that of sugar.

33-

Amount of heat required to raise the temperatire of a substance is calculated by the formula-

Heat = mass of the substance * specific heat of that substance * temp change

So putting the values,, here heat required to raise the temp of gold from 25 to 175oC is-

Heat = mass of the gold taken * specific heat of gold * (final temp - initial temp)

= 150 g * 0.0308 cal/goC * (175oC - 25oC)

= 150 g * 0.0308 cal/goC * 150oC

= 693‬ cal

34-

calories from 15 g protein = 4 kcal/g * 15 g = 60 kcal

calories from 1 g fat = 9 kcal/g * 1 g = 9 kcal

calories from 42 g carbohydrate = 4 kcal/g * 42 g = 168‬ kcal

So total calorie from 1 cup of kidney beans = 60 kcal + 9 kcal + 168‬ kcal

= 237‬ kcal